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PubMed1986

Endocytosis via galactose receptors in vivo. Ligand size directs uptake by hepatocytes and/or liver macrophages.

We followed the intrahepatic binding and uptake of variously sized ligands with terminal galactosyl residues in rat livers. The ligands were administered to prefixed livers in binding studies and in vivo and in situ (serum-free perfused livers) in uptake studies. Gold sols with different particle diameters were prepared: 5 nm (Au5), 17 nm (Au17), 50 nm (Au50) and coated with galactose exposing glycoproteins (asialofetuin (ASF) or lactosylated BSA (LacBSA)). Electron microscopy of mildly prefixed livers perfused with LacBSA-Au5 in serum-free medium showed ligand binding to liver macrophages, hepatocytes and endothelial cells. Ligands bound to prefixed cell surfaces reflect the initial distribution of receptor activity: pre-aggregated clusters of ligands are found on liver macrophages, single particles statistically distributed on hepatocytes and pre-aggregated clusters of particles restricted to coated pits on endothelial cells. Ligand binding is prevented in the presence of 80 mM N-acetylgalactosamine (GalNAc), while N-acetylglucosamine (GlcNAc) is without effect. Electron microscopy of livers after ligand injection into the tail vein shows that in vivo uptake of electron-dense galactose particles by liver cells is size-dependent. Using a LacBSA-Au preparation with heterogeneous particle diameter (2.2-11.7 nm) we found that hepatocytes take up only ligands up to the size of 7.8 nm, whereas particles of all sizes available in this experiment are found in liver macrophages and endothelial cells. ASF-Au17 and LacBSA-Au17 are endocytosed by liver macrophages and endothelial cells, but not by hepatocytes. ASF-Au50 is taken up by liver macrophages only. In vivo uptake by liver macrophages is mediated by galactose-specific recognition as shown by inhibition with GalNAc. Some 52-65% inhibition was measured in in vivo experiments and 78% inhibition in in situ experiments. GlNAc showed no inhibitory effect. Furthermore, we measured uptake of [125J]ASF and of [125J]ASF adsorbed to Au17 by the different cell populations of rat livers in vivo. While the bulk of the molecular ligand is found in the hepatocyte fraction, the particulate ligand is located in the sinusoidal fraction.

Animals↗
PubMed1984

Cytoarchitectural changes in lens epithelium of galactose-fed rats.

Whole mounts of lens epithelia from rats fed on a galactose-rich diet for one, two, three or seven days were examined for morphological alterations. The meridional rows of epithelia from lenses of animals fed on galactose for seven days were found to be grossly disorganized or abnormally elongated. There was some indication that the cells were edematous and that the epithelium had become multilayered. These abnormalities apparently extended into the transitional zone. Evidence of the cytoarchitectural changes was present as early as one day after institution of the 30% galactose diet and progressed steadily over the period of observation. The findings provide support for the hypothesis that loss of meridional row integrity is a phenomenon common to development of most types of cortical cataracts.

Animals↗
PubMed1990

D-[3H]galactose incorporation into glycogen in retinal cone cells.

Previous studies have shown that bovine retinas incubated with [3H]galactose incorporated it, unmodified, into large molecules. Light and electron microscope autoradiography showed a significant proportion of the label to be in cone inner segments, and pulse-chase studies showed it was subsequently transported to the synaptic pedicles. In this report, evidence is presented to show that the galactose-labelled macromolecules are resistant to hydrolysis by proteolytic enzymes, testicular hyaluronidase, chondroitinase ABC, beta-glucosidase and beta-glucuronidase, but are readily degraded by alpha-amylase and beta-galactosidase, and to a lesser extent by beta-amylase. Treatment with alpha-amylase also leads to specific removal of radioactivity from cone inner segments and pedicles, as judged by light-microscopic autoradiography. These studies appear to indicate that the cone-specific galactose label is in glycogen or glycogen-like molecules.

Animals↗
PubMed1990

Ibuprofen, a putative anti-cataract drug, protects the lens against cyanate and galactose.

Cataract, the major cause of blindness world-wide, may be caused partly by modification of lens proteins by carbamylation and non-enzymic glycosylation (glycation) in some patients. Aspirin has been found to protect against these modifications and to prevent cyanate-induced opacification occurring in whole rate lenses. Ibuprofen is an aspirin-like anti-inflammatory drug which appeared as a protective factor against cataract in an Oxford case-control study. The binding of cyanate, galactose and glucose 6-phosphate to lens proteins, and the effect of ibuprofen on this reaction was investigated, as was cyanate-induced opacification in whole rat lenses. Labelled metabolite was incubated with bovine lens homogenate in the presence and absence of ibuprofen, and the incorporation of label into the lens homogenate was followed. Simultaneous and preincubation experiments were performed. Intact rat lenses were incubated in culture medium with and without cyanate and ibuprofen. The phase separation temperature was noted as the temperature at which opacity first appeared on cooling. Cyanate, galactose and glucose 6-phosphate bind progressively to lens proteins. Simultaneous incubation with ibuprofen reduces cyanate and galactose binding but not glucose 6-phosphate. Ibuprofen protects against opacities due to cyanate-induced phase separation. Ibuprofen has protected against cataract in the models of cataractogenesis in this study. It appears to have a different mechanism of action from that of aspirin. These studies provide some support for the idea, based on epidemiological findings, that ibuprofen might be a useful anti-cataract drug.

Animals↗
PubMed1991

Evaluation of lens epithelial cell differentiation by quantitation of MP26 mRNA relative to gamma-crystallin mRNA in initiation of galactose cataracts in the rat.

It is well established that in response to feeding of galactose to four-week-old rats cataracts develop (Unakar, Genyea, Reddan & Reddy, Exp. Eye Res. 26, 123-33, 1978). Initiation of cataracts leads to epithelial cell proliferation. In the lens, the main intrinsic membrane protein, MP26, is recognized as a fiber cell-specific gene product, and gamma-crystallin is found in terminally differentiated fiber cells. By Northern blot analysis we quantitated the MP26 and gamma-crystallin mRNAs found in the lens at various times spanning from 0 to 96 hr on galactose. We find that by 24 hr, MP26 mRNA, as well as gamma-crystallin mRNA, increased significantly above the zero time levels. The data was also confirmed by in situ hybridization of various lens sections to both gamma-crystallin and MP26 35S-labeled antisense RNA probes. As expected, at later periods beyond 24 hr, the levels of gamma-crystallin and MP26 mRNAs dropped to below the control levels. The initial increase in MP26 and gamma-crystallin mRNAs lead us to conclude that initiation of galactose cataracts appears to support, although for a short time period, both epithelial cell elongation and fiber cell differentiation.

Animals↗
PubMed1992

Changes of glutathione and taurine concentrations in lenses of rat eyes induced by galactose-cataract formation or ageing.

Sulphur-containing compounds in the lens were studied in relation to galactose cataract formation. Female Wistar rats were fed a 35% galactose diet and the changes in lens sulphur concentration and its distribution on a gel filtration column were compared with age-related changes. Concentration of sulphur in the whole lens decreased with time. A low constant level was attained on the fifth day of the galactose diet. A decrease of sulphur concentration in the soluble fraction of the lens paralleled that of the whole lens which was correlated with the decrease of glutathione and taurine concentrations on a gel filtration column by high-performance liquid chromatography-inductively coupled argon plasma atomic emission spectrometry (HPLC-ICP). Concentration of magnesium in the lens decreased after the fifth day, while the ratio of sodium to potassium increased. These changes in sulphur-containing compounds and metals were observed prior to the onset of cataract formation.

Aging↗
PubMed1992

Purification of the MglC/E membrane proteins of the binding protein-dependent galactose transport system of Salmonella typhimurium.

The high affinity galactose transport system of Salmonella typhimurium consists of four proteins, a periplasmic galactose binding protein (the MglB protein), and three inner membrane-associated proteins, the MglA, MglC and MglE proteins. We purified the MglC/E proteins from an MglC/E hyperproducing strain after solubilisation of inclusion bodies in guanidine hydrochloride followed by renaturation in a detergent-containing buffer and affinity chromatography on a MglB-Sepharose column. The MglC/E proteins are devoid of ATPase activity and they complement an extract from a strain carrying a plasmid with the mglA gene for reconstitution of the MglB-dependent galactose transport in proteoliposomes.

Bacterial Proteins↗
PubMed1994

Exposure to galactose oxidase of GM1 ganglioside molecular species embedded into phospholipid vesicles.

The exposure of GM1 molecular species present in the native ganglioside, carrying C18:1 or C20:1 long-chain bases (LCB), to Dactylium dendroides galactose oxidase was studied. When native GM1 (49.3% C18:1 and 50.7% C20:1 LCB, respectively), was inserted in dipalmitoylphosphatidylcholine vesicles and partially oxidized (10%), the proportion of C18:1 and C20:1 species in the oxidized GM1 was 59.6% and 40.4%, respectively, suggesting a preferential action of the enzyme on the shorter species. The Vmax of the enzyme was higher on C18:1 GM1 than on C20:1 GM1. The molecular species were affected without any preference after partial (10%) oxidation of GM1 incorporated in egg phosphatidylcholine vesicles or in micellar form. These data indicate that the exposure of the terminal galactose moiety of GM1 ganglioside to galactose oxidase is affected by the ganglioside ceramide composition as well as the phospholipid environment, that presumably determine the distribution (molecular dispersion, segregation) of the ganglioside within the membrane.

Animals↗
PubMed1988

Compared roles of glucose, galactose and fructose as glycogen precursors during the acute response to insulin in cultured rat foetal hepatocytes.

1. The efficiency of the contribution of hexoses to basal- and stimulated-glycogenesis, when studied in cultured 18 day-old rat foetal hepatocytes in the presence of glucose, was as follows: galactose greater than glucose greater than fructose. 2. Glucose deprivation had opposite effects on the contributions of [14C]galactose (decreased) and [14C]fructose (increased) to glycogenesis, which occurred independently of insulin and were reversed by glucose concentrations as low as 30-100 microM. 3. The stimulation of glycogenesis by insulin measured with [14C]glucose (3.2-fold) was superior to that obtained with either [14C]galactose or [14C]fructose (2.7-fold in both cases), which revealed a specific beneficial effect of insulin on glucose contribution.

Animals↗
PubMed1994

The formation of a dimeric product of raffinose by the action of galactose oxidase.

1. Galactose oxidase is known to catalyze the oxidation of the C-6 hydroxymethyl group of galactose to an aldehyde group. 2. When the products of a galactose oxidase-catalase treatment of raffinose were examined by gel filtration and ion exchange chromatography, we found that in addition to the expected 6"-aldehydroaffinose, two other components were present. 3. One component was neutral and had an elution volume close to that of maltopentaose and on treatment with sodium borohydride or hypoiodite, this component was converted to raffinose or 6"-carboxyraffinose, respectively. 4. Fast atom bombardment mass spectroscopy in the negative mode indicated that the major molecular ion had an M/Z of 1003. 5. These data are consistent with this component being a dimer of 6"-aldehydoraffinose.

Catalysis↗
PubMed1983

Peripheral nerve conduction studies in galactose-poisoned rats. Demonstration of increased resistance to ischemic conduction associated with endoneurial edema due to sugar alcohol accumulation.

Edematous nerves of galactose-poisoned rats had an increased resistance to ischemic conduction block when compared with control animals. Ischemia was caused by cardiac arrest due to intracardiac air embolism in 1 group and by occlusion of the abdominal aorta in another. In these 2 groups of galactose-fed rats, time to 50% conduction block was increased by 27 and 42%, respectively and the difference between control and galactose rats was significant (P less than 0.01 and P less than 0.001).

Animals↗
PubMed1989

Increased urinary prostaglandin excretion in galactose-fed rats.

Increased renal production of prostaglandins (PG) may contribute to the hyperfiltration that accompanies early diabetes. It was postulated that a putative metabolic abnormality of diabetes, ie, increased flux through the polyol pathway, stimulates renal PG production and that this phenomenon can be prevented by aldose-reductase inhibition. To test this hypothesis, the effects of polyol accumulation on urinary excretion rates (UER) of PGE2 and 6-keto-PGF1 alpha were studied, using the galactose-fed rat model. UER of PGE2 and 6-keto-PGF1 alpha were measured in three groups of weanling Wistar male rats. Group 1 was maintained on normal chow (n = 6), group 2 was fed chow supplemented with 30% galactose (n = 6), and group 3 received chow supplemented with 30% galactose and 0.7% sorbinil (n = 6). Ten 24-hour urine samples were obtained from each group between 151 and 240 days on the respective diets. UER of PGE2 (P less than .001) and 6-keto-PGF1 alpha (P less than .01) were higher in group 2 than in group 1. UER of PGE2 (NS) and 6-keto-PGF1 alpha (NS), respectively, were similar in groups 1 and 3. These data indicate that flux through the polyol pathway modulates the UER of PGE2 and 6-keto-PGF1 alpha. This phenomenon may contribute to the glomerular hyperfiltration of early diabetes.

6-Ketoprostaglandin F1 alpha↗
PubMed1986

Characteristics of a galactose-binding hemagglutinin (lectin) from hemolymph of Spodoptera exigua larvae.

Hemolymph from Spodoptera exigua larvae agglutinates rabbit and human O erythrocytes. The agglutinin appears to be naturally occurring i.e., injury (by injection) or injection of larvae with fungal cells does not induce an increase in titer of hemolymph samples. Hemagglutinin activity is destroyed by heat or EDTA, and galactosidic carbohydrates inhibit agglutination of both red blood cell types. The agglutinin was purified by affinity chromatography using an Affi-Gel ovalbumin column. Binding to the column is calcium (cation) dependent. SDS gel electrophoresis shows that the agglutinin is a minor component of whole hemolymph represented by two bands with molecular weights of 30,500 and 31,000 daltons. Fluorescence microscopy using rhodamine-labeled agglutinin indicates that the agglutinin binds to fungal cell wall surfaces known to have galactose residues (e.g., Paecilomyces ochraceus), and that binding is specifically inhibited by galactose. There is no specific binding to fungal walls known to lack galactose residues (e.g., Paecilomyces ochraceus, Nomuraea rileyi). The agglutinin may be involved in the immune response of the insect e.g., by opsonization of microbial (fungal) surfaces which render the invading cells more susceptible to phagocytosis or agglutination.

Animals↗
PubMed1988

Synthesis and rapid purification of UDP-[6-3H]galactose.

UDP[6-3H]galactose of high specificity can be obtained by oxidation of the C-6 hydroxymethyl group of UDP-galactose by galactose oxidase and subsequent reduction by sodium borotritide. One-step purification of the nucleotide sugar involves anion-exchange chromatography on a Pharmacia Mono Q column. Radiolabeled UDP-N-acetylgalactosamine can also be synthesized and purified by this procedure. Both nucleotide sugars can be used for sugar incorporation studies using the appropriate glycosyltransferase.

Chromatography, Ion Exchange↗
PubMed1988

Ricin B chain-containing immunotoxins prepared with heat-denatured B chain lacking galactose-binding ability potentiate the cytotoxicity of a cell-reactive ricin A chain immunotoxin.

Ricin B chain incubated at 37 degrees C in the absence of lactose loses its ability to bind the galactose-containing protein, asialofetuin. Circular dichroism analysis of the B chain during thermal denaturation indicates that the loss of galactose-binding ability by the B chain correlates with limited unfolding of the molecule. As a result of this conformational change, disulfide bonds that are shielded from the solvent by the compact folded structure of the B chain become exposed and the chitobiosyl cores of both N-linked oligomannose chains become susceptible to cleavage by endoglycosidases. The heat-denatured B chain does not enhance the toxicity of a ricin A chain-containing rabbit anti-human immunoglobulin (RAHIg-A) to Daudi cells. However, when heat-denatured B chain is coupled to goat anti-rabbit immunoglobulin (GARIg), the resulting immunotoxin, GARIg-hdB, potentiates the killing of RAHIg-A-treated Daudi cells to an extent similar to that of an immunotoxin prepared with GARIg and native B chain. These results indicate that the native, galactose-binding structure of the B chain is not necessary to enhance the cytotoxicity of the cell-reactive A chain immunotoxin (IT-A) and suggests that regions of the B chain exposed by unfolding the molecule may mediate potentiation of cytotoxicity.

Adjuvants, Immunologic↗
PubMed1993

Antigenicity, immunogenicity and vaccine efficacy of the galactose-specific adherence protein of Entamoeba histolytica.

Entamoeba histolytica is an enteric protozoan that causes amoebic colitis and liver abscess. Human immunity to E. histolytica is apparently mediated by a serum antibody response and amoebicidal cellular mechanisms. The galactose-specific adherence protein of E. histolytica is a 260 kDa glycoprotein which mediates amoebic in vitro adherence to human colonic mucins, epithelium, and inflammatory cells. Amoebic lysis of cells is dependent upon binding by this adherence protein. Serum IgG and salivary IgA antibodies from greater than 90% of subjects with invasive amoebiasis recognize the adherence protein's 170 kDa heavy subunit. Incubation of peripheral blood mononuclear cells from antibody-positive subjects with the purified galactose-specific adherence protein induces in vitro T lymphocyte proliferation, IL-2 and gamma interferon production, and direct lymphocyte amoebicidal activity. The rationale for an adherence protein vaccine includes sIgA blockage of amoebic binding to colonic mucins, humoral IgG prevention of parasitic adherence in tissues, and development of amoebicidal cell-mediated immunity. Immunization of gerbils with purified adherence protein in Freund's adjuvant provides protection against intrahepatic challenge with the trophozoites. In summary, the galactose specific adherence protein of E. histolytica contains highly conserved B- and T-cell epitopes, and has a high degree of vaccine efficacy in the gerbil model of amoebic liver abscess.

Animals↗
PubMed1992

Nonviability of cells with oxidative defects in galactose medium: a screening test for affected patient fibroblasts.

Diagnosis of respiratory chain defects in cultured skin fibroblasts is a difficult diagnostic procedure. We investigated the feasibility of using survival of skin fibroblasts in culture medium with galactose as the major carbon source as a method of quickly diagnosing cell lines that were compromised in oxidative metabolism. We found that cells from patients with most forms of cytochrome oxidase deficiency, cells with complex I deficiency, cells with multiple respiratory chain defects and cells with severe pyruvate dehydrogenase (PDH) complex deficiency failed to survive when subcultured into galactose (5 mM) medium. Cells from patients with Lebers hereditary optic neuropathy (LHON), Kearns-Sayre syndrome (KSS), myoclonus-epilepsy-lactic acidosis-stroke (MELAS), the hepatic form of cytochrome oxidase deficiency, and mild PDH complex deficiency survived well in galactose (5 mM)-containing medium. This could be used as a rapid screening test for skin fibroblasts with major oxidative defects.

Cell Line↗
PubMed1994

Binding of glucose, galactose and pyridoxal phosphate to lens crystallins.

Glycation of proteins plays an important role in diabetic complications. Both glucose and galactose were shown to bind progressively to lens crystallins with decreased binding in the presence of increasing concentrations of pyridoxal 5-phosphate (PLP). In longer term incubations (10 mM sugar for 21 days) glucose produced no significant yellowing of the protein, that is no detectable advanced glycation products, but pyridoxal phosphate (15 mM) caused an increased absorbance at 325 nm. This increase was greater in the presence of glucose. It appears that PLP becomes firmly attached to the protein and that this binding is enhanced in the presence of glucose or galactose. Changes produced by sodium borohydride indicate that the PLP is attached to protein amino groups as a Schiff base. Incubation of lens crystallins with PLP also led to increased fluorescence which was greater when sugar was present. However, borohydride experiments indicated that glucose and galactose may decrease the formation of non-reducible adducts of PLP. The decreased glycation in the presence of PLP supports the notion that it might be useful in prevention of diabetic complications, but the reaction of PLP itself with protein is less encouraging.

Animals↗