Biomedical subjects

Thisbe K Lindhorst

Publications and source records attributed to Thisbe K Lindhorst.

9 recordsLinked to original sources

PubMed2006

Oligomannoside mimetics by glycosylation of 'octopus glycosides' and their investigation as inhibitors of type 1 fimbriae-mediated adhesion of Escherichia coli.

The glycocalyx of eukaryotic cells is composed of glycoconjugates, which carry highly complex oligosaccharide portions. To elucidate the biological role and function of the glycocalyx in cell-cell communication and cellular adhesion processes, glycomimetics have become targets of glycosciences, which resemble the composition and structural complexity of the glycocalyx constituents. Here, we report about the synthesis of a class of oligosaccharide mimetics of a high-mannose type, which were obtained by mannosylation of spacered mono- and oligosaccharide cores. These carbohydrate-centered cluster mannosides have been targeted as inhibitors of mannose-specific bacterial adhesion, which is mediated by so-called type 1 fimbriae. Their inhibitory potencies were measured by ELISA and compared to methyl mannoside as well as to a series of mannobiosides, and finally to the polysaccharide mannan. The obtained results suggest a new interpretation of the mechanisms of bacterial adhesion according to a macromolecular rather than a multivalency effect.

Bacterial Adhesion↗

PubMed2006

Evaluation of the carbohydrate recognition domain of the bacterial adhesin FimH: Design, synthesis and binding properties of mannoside ligands.

Fimbriae are proteinogeneous appendages on the surface of bacteria, which mediate bacterial adhesion to the host cell glycocalyx. The so-called type 1 fimbriae exhibit specificity for alpha-d-mannosides and, therefore, they are assumed to mediate bacterial adhesion via the interaction of a fimbrial lectin and alpha-d-mannosyl residues exposed on the host cell surface. This carbohydrate-specific adhesive protein subunit of type 1 fimbriae has been identified as a protein called FimH. The crystal structure of this lectin is known and, based on this information, the molecular details of the interaction of mannoside ligands and FimH are addressed in this paper. Computer-based docking methods were used to evaluate known ligands as well as to design new ones. Then, a series of new mannosides with extended aglycon was synthesized and tested as inhibitors of type 1 fimbriae-mediated bacterial adhesion in an ELISA. The results obtained were compared to the predictions and findings as delivered by molecular modeling. This study led to an improved understanding of the ligand-receptor interactions under investigation.

Adhesins, Escherichia coli↗

PubMed2006

Multivalent glycomimetics: synthesis of nonavalent mannoside clusters with variation of spacer properties.

Oligosaccharide mimetics are important tools in the glycosciences. In this work, we have employed spaced glycodendrons for the synthesis of oligomannoside mimetics. Starting from a number of trivalent, branched molecular wedges, the preparation of nonavalent cluster mannosides was accomplished, which were varied with regard to the chemical characteristics of their spacer moieties and spacer lengths. For ligation of the various trivalent dendrons to the nonavalent target molecules peptide coupling was employed.

Bacterial Adhesion↗

PubMed2004

Glucuronic acid derivatives as branching units for the synthesis of glycopeptide mimetics.

Natural glycopeptides and glycoproteins exhibit a large structural diversity, which can be mimicked by synthetic glycopeptide derivatives to assist the investigation of biological functions and structure-activity relationships. Here, dendronized saccharides were synthesized to provide glycosyl amino acids, equipped with a branching element for the preparation of branched glycopeptide mimetics. An optimized Staudinger-type reaction served as key reaction en route to the complex glycopeptide 14, in which three mannose moieties were connected to the branched glucuronyl scaffold.

Amino Acids↗

PubMed2004

Functional evaluation of carbohydrate-centred glycoclusters by enzyme-linked lectin assay: ligands for concanavalin A.

The affinities of the mannose-specific lectin concanavalin A (Con A) towards D-glucose-centred mannosyl clusters differing in the anomeric configuration of the monosaccharide core, nature of the bridging functional groups and valency, have been measured by a competitive enzyme-linked lectin assay. Pentavalent thioether-linked ligands (5 and 7) were prepared by radical addition of 2,3,4,6-tetra-O-acetyl-1-thio-alpha-D-mannopyranose to the corresponding penta-O-allyl-alpha- or -beta-D-glucopyranose, followed by deacetylation. The distinct reactivity of the anomeric position in the D-glucose scaffold was exploited in the preparation of a tetravalent cluster (10) that keeps a reactive aglyconic group for further manipulation, including incorporation of a reporter group or attachment to a solid support. Hydroboration of the double bonds in the penta-O-allyl-alpha-D-glucopyranose derivative and replacement of the hydroxy groups with amine moieties gave a suitable precursor for the preparation of pentavalent and 15-valent mannosides through the thiourea-bridging reaction (17 and 20, respectively). The diastereomeric 1-thiomannose-coated clusters 5 and 7 were demonstrated to be potent ligands for Con A, with IC(50) values for the inhibition of the Con A-yeast mannan association indicative of 6.4- and 5.5-fold increases in binding affinity (valency-corrected values), respectively, relative to the value for methyl alpha-D-mannopyranoside. The tetravalent cluster 10 exhibited a valency-corrected relative lectin-binding potency virtually identical to that of the homologous pentavalent mannoside 7. In sharp contrast, replacement of the 1-thiomannose wedges of 5 with alpha-D-mannopyranosylthioureido units (17) virtually abolished any multivalent or statistic effects, with a dramatic decrease of binding affinity. The 15-valent ligand 20, possessing classical O-glycosidic linkages, exhibited a twofold increase in lectin affinity relative to the penta-O-(thioglycoside) 5; it is less efficient based on the number of mannose units. The results illustrate the potential of carbohydrates as polyfunctional platforms for glycocluster construction and underline the importance of careful design of the overall architecture in optimising glycocluster recognition by specific lectins.

Binding Sites↗

PubMed2004

Fluorescent labelled thiourea-bridged glycodendrons.

GlcNAc-coated glycodendrimers, which are polyvalent glycomimetics, display strong in vitro affinity for the rat natural killer cell protein-1A (NKR-P1A), a C-type lectin-like receptor of natural killer (NK) cells in rats, humans and some strains of mice. Administration of these compounds in vivo results in a substantial increase in the antitumour activity with involvement of the natural cell immunity. To clarify the in vitro and in vivo fate of these molecules, we synthesized labelled glycodendron analogues of the previously studied glycodendrimers. Labelling with fluorescent tags enabled the localization of the glycodendrons in white blood cells, tumours and other tissues by using different imaging techniques such as fluorescence and confocal microscopy. These studies are useful for probing the mechanism of action and fate of artificial ligands and the cell receptors involved.

Animals↗

PubMed2003

Effects of N-acetyl-glucosamine-coated glycodendrimers as biological modulators in the B16F10 melanoma model in vivo.

Glyco-coat changes on cancer cells due to aberrant glycosylation are potential targets for immune recognition through lectin-like receptors on immune cells. These cells include natural killer (NK), CD8+ and CD4+ lymphocytes, all reported to have, together with cytokines, important functions in antitumor immunity. The aim of this study was to evaluate a possible role of synthetic monodisperse multivalent neo-glycoconjugates, namely glycodendrimers, as a new approach to anticancer immune modulation through carbohydrate-mediated immune recognition. Octavalent polyamidoamine dendrimers functionalized with N-acetyl-glucosamine residues (PAMAM-GlcNAc8), with in vitro high affinity for the recombinant lymphocyte receptor NKR-P1A, were employed. To follow the fate of the compound, a fluorescent marker was conjugated to the tetra-branched semi-component of the dendrimer. Tumor development and immunity were evaluated in C57BL/6 mice. Animals were inoculated with B16F10 melanoma cells and underwent different protocols of PAMAM-GlcNAc8 administration. Advantages on survival and reduction of tumor growth were obtained in dose-dependent manner, by IP route. Increase of CD69+ cells in the spleen and their appearance inside the tumors, early progressive release of IL-1beta, a later production of INFgamma and IL-2 concomitant to an increment of CD4+ cells were observed. Cytotoxicity assays, performed ex vivo, showed an enhanced NK cell activity proportioned to the percentage of activated NK cells. Our data suggest that well-defined multivalent neo-glycoconjugates can stimulate an antitumor immune response engaging both innate and acquired immunity.

Acetylglucosamine↗

PubMed2002

Molecular dynamics simulations of glycoclusters and glycodendrimers.

Protein-carbohydrate recognition plays a crucial role in a wide range of biological processes, required both for normal physiological functions and the onset of disease. Nature uses multivalency in carbohydrate-protein interactions as a strategy to overcome the low affinity found for singular binding of an individual saccharide epitope to a single carbohydrate recognition domain of a lectin. To mimic the complex multi-branched oligosaccharides found in glycoconjugates, which form the structural basis of multivalent carbohydrate-protein interactions, so-called glycoclusters and glycodendrimers have been designed to serve as high-affinity ligands of the respective receptor proteins. To allow a rational design of glycodendrimer-type molecules with regard to the receptor structures involved in carbohydrate recognition, a deeper knowledge of the dynamics of such molecules is desirable. Most glycodendrimers have to be considered highly flexible molecules with their conformational preferences most difficult to elucidate by experimental methods. Longtime molecular dynamics (MD) simulations with inclusion of explicit solvent molecules are suited to explore the conformational space accessible to glycodendrimers. Here, a detailed geometric and conformational analysis of 15 glycodendrimers and glycoclusters has been accomplished, which differ with regard to their core moieties, spacer characteristics and the type of terminal carbohydrate units. It is shown that the accessible conformational space depends strongly on the structural features of the core and spacer moieties and even on the type of terminating sugars. The obtained knowledge about possible spatial distributions of the sugar epitopes exposed on the investigated hyperbranched neoglycoconjugates is detailed for all examples and forms important information for the interpretation and prediction of affinity data, which can be deduced from biological testing of these multivalent neoglycoconjugates.

Carbohydrate Conformation↗

PubMed2002

Dendrimers.

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Animals↗