Search PubMed⌕ Search

Biomedical subjects

Raymond A Dwek

Publications and source records attributed to Raymond A Dwek.

At least 127 records · Page 7Linked to original sources
PubMed2002

"Internal residue loss": rearrangements occurring during the fragmentation of carbohydrates derivatized at the reducing terminus.

Rearrangement reactions involving migration of fucose and, occasionally, other residues have been found in the CID spectra of [M + H]+ and [M + 2H]2+ ions, but not [M + Na]+ ions, generated from several O-linked carbohydrates and milk sugars derivatized at their reducing termini with aromatic amines such as 2-aminobenzamide. Such rearrangements, which are similar to those reported by other investigators from several underivatized carbohydrates and glycosides, cause an apparent loss of sugar residues from within a carbohydrate chain and can produce ambiguous results during spectral interpretation. A mechanism, involving initial protonation of the amine nitrogen atom of the derivative, is proposed to account for the formation of the observed ions.

Amines↗
PubMed2002

Modulation of THP-1 macrophage and cholesterol-loaded foam cell apolipoprotein E levels by glycosphingolipids.

Macrophages synthesize and secrete apolipoprotein E (apoE) constitutively. This process is upregulated under conditions of cholesterol loading. The response to cholesterol is antiatherogenic as it is believed to promote cholesterol efflux from the artery wall. The concentration of lactosyl ceramide (LacCer), a glycosphingolipid recently discovered to regulate cellular signaling, proliferation, and expression of adhesion molecules, is also increased in atherosclerotic tissues. Here we have investigated the effect of exogenous LacCer on macrophage apoE levels. We show that increasing macrophage LacCer levels sevenfold led to reductions in cellular and secreted apoE (15 and 30%, respectively, over a 24-h period) as determined by enzyme-linked immunosorbent assay. A similar effect was also induced by glucosyl ceramide (GlcCer) but not by ganglioside species. When macrophages were converted to cholesterol-loaded foam cells by incubation with acetylated LDL, the resulting increase in cellular apoE levels was inhibited by 26% when the cells were subsequently enriched with LacCer. After metabolic labeling of cellular glycosphingolipids with [14C]palmitate, we also discovered that high-density lipoprotein (HDL) stimulates the efflux of glycosphingolipids from foam cells. These data imply that LacCer and GlcCer may be proatherogenic due to the suppression of macrophage apoE production. Furthermore, the efflux of glycosphingolipids from macrophage foam cells to HDL could indicate a potential pathway for their removal from the artery wall and subsequent delivery to the liver.

Apolipoproteins E↗
PubMed2002

Towards complete analysis of the platelet proteome.

Platelets exert a crucial function in haemostasis, wound repair, and the formation of vascular plugs, underlying thrombotic diseases such as stroke and myocardial infarction. Analysis of platelet biochemistry is largely dependent on protein analysis as platelets are anucleated cells providing little analytical target for DNA or RNA based strategies. Here we present data from our analysis of the human platelet proteome, the entire set of proteins building a platelet at a given point in time. Proteins were separated by two-dimensional electrophoresis (2-DE) using broad and narrow range pH gradients in the isoelectric focusing step. Consequently, a high-resolution 2-DE proteome map has been generated that comprises approximately 2300 different protein features. From the 536 protein features detected in the 4-5 pI range 284 features were identified by electrospray ionisation time of flight tandem mass spectrometry. These 284 proteins originate from 123 different open reading frames. This includes the five human proteins KIAA0193, KIAA0573, KIAA0830, WUGSC:H_DJ0777O23 protein, and cytokine receptor related protein 4, all isolated for the first time. The data are discussed with regard to proteome characteristics, protein function, and the high prevalence of signalling molecules. This study contributes to a more thorough and holistic understanding of platelet biology, helping to build the basis for future identification of new drug targets and therapeutic strategies.

Blood Platelets↗
PubMed2002

The carbohydrate moiety of serum IgM from Atlantic cod (Gadus morhua L.).

The carbohydrate moiety of cod serum IgM was analysed using oligosaccharide sequencing techniques. The carbohydrate moiety constituted about 10% of the molecular weight of cod IgM, was associated with the constant region of the heavy chains (Fc), and was composed of N-linked complex type oligosaccharides. Considerable heterogeneity was observed. Sixteen different glycan structures were identified, over 60% were sialylated and 40% contained core fucose. The carbohydrate moiety of cod IgM was shown to provide protection against protease digestion, and partial deglycosylation abolished the antigen binding property of natural cod anti-TNP-BSA antibody.

Animals↗
PubMed2002

An inducible mouse model of late onset Tay-Sachs disease.

Mouse models of the G(M2) gangliosidoses, Tay-Sachs and Sandhoff disease, are null for the hexosaminidase alpha and beta subunits respectively. The Sandhoff (Hexb-/-) mouse has severe neurological disease and mimics the human infantile onset variant. However, the Tay-Sachs (Hexa-/-) mouse model lacks an overt phenotype as mice can partially bypass the blocked catabolic pathway and escape disease. We have investigated whether a subset of Tay-Sachs mice develop late onset disease. We have found that approximately 65% of the mice develop one or more clinical signs of the disease within their natural life span (n = 52, P < 0.0001). However, 100% of female mice with repeat breeding histories developed late onset disease at an earlier age (n = 21, P < 0.0001) and displayed all clinical features. Repeat breeding of a large cohort of female Tay-Sachs mice confirmed that pregnancy induces late onset Tay-Sachs disease. Onset of symptoms correlated with reduced up-regulation of hexosaminidase B, a component of the bypass pathway.

Age of Onset↗
PubMed2002

The combination of interferon alpha-2b and n-butyl deoxynojirimycin has a greater than additive antiviral effect upon production of infectious bovine viral diarrhea virus (BVDV) in vitro: implications for hepatitis C virus (HCV) therapy.

Interferon alpha-2b (IFN) alone or in combination with Ribavirin is approved in the United States for the treatment of chronic hepatitis C virus (HCV) infection. We have previously reported that the glucosidase inhibitor, n-butyl deoxynojirimycin (nB-DNJ) inhibits the production of infectious bovine diarrhea virus (BVDV) (Proc. Natl. Acad. Sci. 96 (1999) 11878). Since BVDV has been used as a model for HCV and grows productively in tissue culture, and IFN and glucosidase inhibitors are thought to act at different steps in the virus life cycle, it was of interest to determine the antiviral impact of combining nB-DNJ with IFN. Using plaque reduction and single-step growth analyses of the cytopathic BVDV strain NADL, data are presented that shows human IFN inhibited BVDV production in a dose dependent manner, with 3 IU/ml inhibiting 50% of the yield of virus (IC50) when added within 1 h post infection. Under the same conditions, the glucosidase inhibitors nB-DNJ and castanospermine (CST) also prevented BVDV production in a dose dependent manner with IC50s of 226 microM and 47 microM, respectively. In combination with 138 microM nB-DNJ the apparent IC50 for IFN was 0.056 IU/ml. This 54-fold increase in IFN potency suggests that nB-DNJ can synergize with IFN. Two additional independent analyses were performed to measure combination effects which demonstrated that the combined antiviral effect of nB-DNJ and IFN were greater than would be expected for a simple additivity. These data are consistent with an interpretation that glucosidase inhibitors and IFN have a synergistic antiviral effect in tissue culture. The relevance of these finding to treatment of HCV infection is discussed.

1-Deoxynojirimycin↗
PubMed2002

Glycosylation and prion protein.

Recent advances have elucidated the detailed glycosylation of the prion protein and highlighted the size of the sugars, which shield large areas of the protein and confer some conformational stability on the normal cellular form. The reliability of SDS-PAGE banding patterns of different "glycoforms" as a diagnostics tool has been discussed. The possibility exists that the glycans may play a role in the location of the prion protein on the neuronal cell surface. Alternative topologies and tethering of the prion glycoprotein on the cell membrane affect glycan site occupancy and may play a role in disease pathogenesis.

Glycosylation↗
PubMed2002

Targeting glycosylation as a therapeutic approach.

Increased understanding of the role of protein- and lipid-linked carbohydrates in a wide range of biological processes has led to interest in drugs that target the enzymes involved in glycosylation. But given the importance of carbohydrates in fundamental cellular processes such as protein folding, therapeutic strategies that modulate, rather than ablate, the activity of enzymes involved in glycosylation are likely to be a necessity. Two such approaches that use imino sugars to affect glycosylation enzymes now show considerable promise in the treatment of viral infections, such as hepatitis B, and glucosphingolipid storage disorders, such as Gaucher disease.

Animals↗
PubMed2002

Biochemistry and molecular biology of gelatinase B or matrix metalloproteinase-9 (MMP-9).

The matrix metalloproteinases (MMPs) form an enzyme family of which gelatinase B (MMP-9) represents the largest and most complex member. We focus here on the biochemical properties, regulation, and functions of gelatinase B. The tight regulation of gelatinase B activity is highly complex and is established at five different levels. The transcription of the gelatinase B-gene depends on various cis-elements in its gene promotor and is induced or repressed by a large variety of soluble factors, including cytokines, growth factors, and hormones and by cellular contacts acting through specific signaling pathways. The specific regulation of its secretion occurs in cells storing gelatinase B in granules. After secretion, progelatinase B must be activated through an activation network. The enzyme activity is further regulated by inhibition and by other mechanisms, such as fine-tuning and stabilization by glycosylation. The ability of gelatinase B to degrade components of the extracellular matrix and to regulate the activity of a number of soluble proteins confers an important role in various physiological and pathological processes. These include reproduction, growth, development, inflammation, and vascular and proliferative diseases.

Animals↗
PubMed2002

Localization and characterization of polysialic acid-containing N-linked glycans from bovine NCAM.

The neural cell adhesion molecule (NCAM) plays important roles during development, plasticity, and regeneration in the adult nervous system. Its function is strongly influenced by attachment of the unusual alpha 2-8-linked polysialic acid (PSA). Here we analyzed the N-glycosylation pattern of polysialylated NCAM from brains of newborn calves. Purified PSA-NCAM glycoprotein was digested with trypsin, and PSA-glycopeptides were separated by immunoaffinity chromatography. For determining the N-glycosylation sites, PNGase F-treated glycopeptides were analyzed by Edman degradation and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). They were found to be exclusively linked to the fifth (Asn 439) and sixth (Asn 468) N-glycosylation sites in the fifth immunoglobulin-like domain of NCAM. The chain length of PSA consisted of at least 30 sialic acid residues, as shown by anion exchange chromatography. For analysis of the core structures, endoneuraminidase N-treated PSA-NCAM was separated by SDS-PAGE and digested with PNGase F. The core structures of polysialylated glycans were characterized by MALDI-MS combined with exoglycosidase digestions and chromatographic fractionation. They include hybrid, di-, tri-, and small amounts of tetraantennary carbohydrates, which were all fucosylated at the innermost N-acetylglucosamine. For the triantennary glycans, the "2,6" arm was preferred in polysialylated structures. High levels of sulfated groups were found on polysialylated structures and to a lower extent also on nonpolysialylated glycans. In addition, high-mannose-type glycans could be detected on PSA-NCAM glycoforms ranging from (GlcNAc)(2)(Man)(5) up to (GlcNAc)(2)(Man)(9). In conclusion, we observed a structural variability and high regional selectivity for the PSA-glycans attached to the NCAM molecule that are most likely influencing its biological functions.

Animals↗
PubMed2002

Comparison of the N-linked glycans from soluble and GPI-anchored CD59 expressed in CHO cells.

The N-linked glycosylation of recombinant human CD59, expressed in Chinese hamster ovary (CHO) cells with and without a membrane anchor, was compared to examine the effect of the anchor on glycan processing. N-Linked glycans were released with peptide-N-glycosidase F (PNGase F) within gel from SDS-PAGE-isolated soluble and glycosylphosphatidylinositol (GPI)-anchored human CD59 expressed in CHO cells. The anchored form contained core-fucosylated neutral and sialylated bi-, tri-, and tetraantennary glycans with up to four N-acetyllactosamine extensions. Exoglycosidase digestions and analysis by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry were used to define the relative amounts of the bi-, tri-, and tetraantennary glycans and to investigate the distribution of N-acetyllactosamine extensions between their antennae. Biantennary structures accounted for about 60% of the glycans, 30% of the triantennary structures, and about 10% of the tetraantennary structures. For tri- and tetraantennary glycans, those with extended antennae were found to be more abundant than those without extensions. The soluble form of CD59, expressed in CHO cells without the GPI anchor signal sequence, consisted almost entirely (97%) of biantennary glycans, of which 81% were unmodified, 17% contained one N-acetyllactosamine extension, and 2% contained two extensions. No compounds with longer extensions were found. A MALDI spectrum of the intact glycoprotein showed a distribution of glycans that matched those released with PNGase F. In addition, the protein was substituted with several small glycans, such as HexNAc, HexNAc-->Fuc, and HexNAc-->HexNAc, probably as the result of degradation of the mature N-linked glycans. The results show that the presence of the anchor increases the extent of glycan processing, possibly as the result of longer exposure to the glycosyltransferases or to a closer proximity of the protein to these enzymes.

Amino Acid Sequence↗
PubMed2002

Structure-activity relationship of a new class of anti-hepatitis B virus agents.

N-Nonyl-deoxy-galactonojirimycin (N-nonyl-DGJ) has been shown to reduce the amount of hepatitis B virus (HBV) produced by tissue cultures under conditions where cell viability is not affected. We show here that the compound N-nonyl-DGJ was effective against lamivudine-resistant HBV mutants bearing the YMDD motif in the polymerase gene, consistent with the compound's activity being distinct from those of nucleoside inhibitors. To better understand the chemical structures that influence its antiviral activity, a series of imino sugar derivatives were made and tested for their antiviral activity against HBV. This work suggests that the antiviral activity of the alkovirs requires an alkyl chain length of at least eight carbons but that the galactose-based head group can be modified with little or no loss in activity.

Antiviral Agents↗
PubMed2002

The broadly neutralizing anti-human immunodeficiency virus type 1 antibody 2G12 recognizes a cluster of alpha1-->2 mannose residues on the outer face of gp120.

2G12 is a broadly neutralizing human monoclonal antibody against human immunodeficiency virus type-1 (HIV-1) that has previously been shown to bind to a carbohydrate-dependent epitope on gp120. Here, site-directed mutagenesis and carbohydrate analysis were used to define further the 2G12 epitope. Extensive alanine scanning mutagenesis showed that elimination of the N-linked carbohydrate attachment sequences associated with residues N295, N332, N339, N386, and N392 by N-->A substitution produced significant decreases in 2G12 binding affinity to gp120(JR-CSF). Further mutagenesis suggested that the glycans at N339 and N386 were not critical for 2G12 binding to gp120(JR-CSF). Comparison of the sequences of isolates neutralized by 2G12 was also consistent with a lesser role for glycans attached at these positions. The mutagenesis studies provided no convincing evidence for the involvement of gp120 amino acid side chains in 2G12 binding. Antibody binding was inhibited when gp120 was treated with Aspergillus saitoi mannosidase, Jack Bean mannosidase, or endoglycosidase H, indicating that Man(alpha)1-->2Man-linked sugars of oligomannose glycans on gp120 are required for 2G12 binding. Consistent with this finding, the binding of 2G12 to gp120 could be inhibited by monomeric mannose but not by galactose, glucose, or N-acetylglucosamine. The inability of 2G12 to bind to gp120 produced in the presence of the glucose analogue N-butyl-deoxynojirimycin similarly implicated Man(alpha)1-->2Man-linked sugars in 2G12 binding. Competition experiments between 2G12 and the lectin cyanovirin for binding to gp120 showed that 2G12 only interacts with a subset of available Man(alpha)1-->2Man-linked sugars. Consideration of all the data, together with inspection of a molecular model of gp120, suggests that the most likely epitope for 2G12 is formed from mannose residues contributed by the glycans attached to N295 and N332, with the other glycans playing an indirect role in maintaining epitope conformation.

Amino Acid Sequence↗
PubMed2002

Antiviral effects of an iminosugar derivative on flavivirus infections.

Endoplasmic reticulum (ER) alpha-glucosidase inhibitors, which block the trimming step of N-linked glycosylation, have been shown to eliminate the production of several ER-budding viruses. Here we investigated the effects of one such inhibitor, N-nonyl-deoxynojirimycin (NN-DNJ), a 9-carbon alkyl iminosugar derivative, on infection by Japanese encephalitis virus (JEV) and dengue virus serotype 2 (DEN-2). In the presence of NN-DNJ, JEV and DEN-2 infections were suppressed in a dose-dependent manner. This inhibitory effect appeared to influence DEN-2 infection more than JEV infection, since lower concentrations of NN-DNJ substantially blocked DEN-2 replication. Secretion of the flaviviral glycoproteins E and NS1 was greatly reduced, and levels of DEN-2 viral RNA replication measured by fluorogenic reverse transcription-PCR were also decreased, by NN-DNJ. Notably, the viral glycoproteins, prM, E, and NS1 were found to associate transiently with the ER chaperone calnexin, and this interaction was affected by NN-DNJ, suggesting a potential role of calnexin in the folding of flaviviral glycoproteins. Additionally, in a mouse model of lethal challenge by JEV infection, oral delivery of NN-DNJ reduced the mortality rate. These findings show that NN-DNJ has an antiviral effect on flavivirus infection, likely through interference with virus replication at the posttranslational modification level, occurring mainly in the ER.

1-Deoxynojirimycin↗
PubMed2002

Imino sugars that are less toxic but more potent as antivirals, in vitro, compared with N-n-nonyl DNJ.

Imino sugar glucosidase inhibitors have selective antiviral activity against certain enveloped, mammalian viruses. Deoxynojirimycins (DNJs) modified by N-alkylation to contain a nine carbon atom side chain (N-n-nonyl-deoxynojirimycin; N-nonyl-DNJ, NN-DNJ) were shown to be, for example, at least 20 times more potent in inhibiting hepatitis B virus (HBV) and bovine viral diarrhoea virus (BVDV) in cell based assays than the non-alkylated DNJ. These data suggested that modification of the alkyl side chain could influence antiviral activity. Previous work has focused on varying side chain length. In this report, the influence of side chain branching and cyclization upon toxicity and antiviral activity was explored. Briefly, using a virus secretion assay for HBV and a single step growth (yield reduction) assay for BVDV, 14 different DNJ-based sugars, possessing various N-alkyl substitutions, were tested for antiviral activity. Of the series, N-methoxy-nonyl-DNJ and N-butyl-cyclohexyl DNJ were determined to have the best selectivity index against BVDV and HBV, with the N-methoxy analogue being the most potent with micromolar antiviral activity. The results of this antiviral survey and the implications for the mechanism of action and ultimate therapeutic potential of the DNJ-based imino sugars is provided and discussed.

1-Deoxynojirimycin↗
PubMed2002

Glucosylceramide modulates membrane traffic along the endocytic pathway.

Glycosphingolipids are endocytosed and targeted to the Golgi apparatus, but are mistargeted to lysosomes in numerous sphingolipidoses. Substrate reduction therapy utilizes imino sugars to inhibit glucosylceramide synthase and potentially abrogate the effects of storage. Gaucher disease is a hereditary deficiency in glucocerebrosidase leading to glucosylceramide accumulation; however, Gaucher fibroblasts exhibited normal Golgi transport of lactosylceramide. To better understand the effects of glycosphingolipid accumulation on intracellular trafficking and the use of imino sugar inhibitors, we studied sphingolipid endocytosis in fibroblast and macrophage models for Gaucher disease. Treatment of fibroblasts or RAW macrophages with conduritol B epoxide, an inhibitor of lysosomal glucocerebrosidase, resulted in a change in the endocytic targeting of lactosylceramide from the Golgi to the lysosomes. Co-treatment of macrophages with conduritol B-epoxide and 12-25 microM N-butyldeoxygalactonojirimycin, an inhibitor of glycosphingolipid biosynthesis, prevented the mistargeting of lactosylceramide to the lysosomes and restored trafficking to the Golgi. Surprisingly, higher doses (>25 microM) of NB-DGJ induced targeting of lactosylceramide to the lysosomes, even in the absence of conduritol B-epoxide. These data demonstrate that both increases and decreases in glucosylceramide levels can dramatically alter the endocytic targeting of lactosylceramide and suggest a role for glucosylceramide in regulation of membrane transport.

Biological Transport↗