Intervention with bacterial adhesion by multivalent carbohydrates

High-affinity glycopolymer binding to human DC-SIGN and disruption of DC-SIGN interactions with HIV envelope glycoprotein

Noncovalent interactions between complex carbohydrates and proteins drive many fundamental processes within biological systems, including human immunity. In this report we aimed to investigate the potential of mannose-containing glycopolymers to interact with human DC-SIGN and the ability of these glycopolymers to inhibit the interactions between DC-SIGN and the HIV envelope glycoprotein gp120. We used a library of glycopolymers that are prepared via combination of copper-mediated living radical polymerization and azide-alkyne [3+2] Huisgen cycloaddition reaction. We demonstrate that a relatively simple glycopolymer can effectively prevent the interactions between a human dendritic cell associated lectin (DC-SIGN) and the viral envelope glycoprotein gp120. This approach may give rise to novel insights into the mechanisms of HIV infection and provide potential new therapeutics.

Adaptable synthesis of C-glycosidic multivalent carbohydrates and succinamide-linked derivatization

A modular approach to the synthesis of trivalent C-glycosidic carbohydrates is described. The approach is illustrated employing carboxylate-terminated C-glycosidic d-mannose, d-glucose, and d-galactose derivatives with different length C1-linked spacer units and also core units with different length linker units attached. The central core scaffold is additionally functionalized via a succinamide-based, conjugatable linker unit, exemplified in an extended multivalent derivative [31] and a pyrene-bearing fluorsecent-labeled tris-C-mannosyl conjugate [33].

Multivalent Antimicrobial Peptides as Therapeutics: Design Principles and Structural Diversities

This review highlights the design principles, progress and advantages attributed to the structural diversity associated with both natural and synthetic multivalent antimicrobial peptides (AMPs). Natural homo- or hetero-dimers of AMPs linked by intermolecular disulfide bonds existed in the animal kingdom, but the multivalency strategy has been adopted to create synthetic branched or polymeric AMPs that do not exist in nature. The multivalent strategy for the design of multivalent AMPs provides advantages to overcome the challenges faced in clinical applications of AMPs, such as: stability, efficiency, toxicity, maintenance of activity in high salt concentrations and under physiological conditions, and importantly overcoming bacterial resistance which is currently a leading health problem in the world. The multivalency strategy is valuable for moving multivalent AMPs toward clinical applications.

First characterization of bioactive components in soybean tempe that protect human and animal intestinal cells against enterotoxigenic Escherichia coli (ETEC) infection

Tempe extracts can inhibit the adhesion of enterotoxigenic Escherichia coli (ETEC) to intestinal cells and thereby can play a role in controlling ETEC-induced diarrhea. The component responsible for this adhesion inhibition activity is still unknown. This research describes the purification and partial characterization of this bioactive component of tempe. After heating, defatting, and protease treatment, the extracts were found to remain active. However, after treatment with polysaccharide-degrading enzyme mixtures the bioactivity was lost. Ultrafiltration revealed the active component to be >30 kDa. Further purification of the bioactive tempe extracts yielded an active fraction with an increased carbohydrate content of higher arabinose content than the nonactive fractions. In conclusion, the bioactive component contains arabinose and originates from the arabinan or arabinogalactan side chain of the pectic cell wall polysaccharides of the soybeans, which is probably released or formed during fermentation by enzymatic modifications.

Detection of pathogenic Streptococcus suis bacteria using magnetic glycoparticles

Detection of the zoonotic bacterial pathogen Streptococcus suis was achieved using magnetic glycoparticles. The bacteria contain an adhesion protein for the carbohydrate sequence Galalpha1,4Gal. After incubation with various amounts of the pathogen, magnetic concentration and ATP detection, bacterial levels down to 10(5) cfu could be detected. Submicrometer particles were needed, since with the larger microparticles the method did not succeed.

An efficient modular approach for the assembly of s-linked glycopeptoids

A short and convenient methodology for the synthesis of S-glycosylated peptoid models is described. The thioglycosylated building blocks were prepared from proper peracetylated sugars via glycosyl iodides in a one-pot fashion and directly employed in a submonomer solid-phase stategy.

Blocking of Pseudomonas aeruginosa and Ralstonia solanacearum Lectins by plant and microbial branched polysaccharides used as food additives

Pseudomonas aeruginosa antibiotic resistance prompted the search for glycodecoys that would block its lectin-dependent adhesion to human cells. We have used the lectins of this pathogen, PA-IL (galactophilic LecA) and PA-IIL (fucophilic LecB), and two additional pathogenic bacterial lectins, CV-IIL (fucophilic, of Chromobacterium violaceum) and RS-IIL (mannophilic, of Ralstonia solanacearum), for assaying the pathogenic lectin-blocking abilities of some plant and microbial polysaccharidic food additives, adding the mannophilic plant lectin Con A as a reference. Locust-bean and guar galactomannans and acacia gum very strongly inhibited PA-IL. The other lectins, excluding CV-IIL, were very strongly inhibited by yeast mannan. Xanthan and inulin were weak inhibitors. The differential blocking of these lectins by galactosylated branches of plant polysaccharides and by mannan matched their inhibition by avian egg whites, human milk, and royal jelly (protecting animal embryos and neonates from infections). The nondigestability and nontoxicity of the food additives are advantageous for curing gastrointestinal and external infections.

Polymer-Based Therapeutics

Polymeric materials have been applied in therapeutic applications, such as drug delivery and tissue regeneration, for decades owing to their biocompatibility and suitable mechanical properties. In addition, select polymer-drug conjugates have been used as bioactive pharmaceuticals owing to their increased drug efficacy, solubility, and target specificity compared with small-molecule drugs. Increased synthetic control of polymer properties has permitted the production of polymer assemblies for the targeted and controlled delivery of drugs, and polymeric sequestrants take advantage of their lack of solubility for the sequestration of target molecules in vivo. In more recent studies reviewed in greater detail here, the properties of polymers that distinguish them from small-molecule drugs, such as their high molecular weight and their ability to display multiple pendant moieties, have been specifically exploited for activating cellular targets or inhibiting the binding of pathogens. The elucidation of relevant structure-function relationships in investigations of this kind has relied on the combination of living polymerization methods with chemical conjugation methods, and protein engineering methods have shown increasing potential in the manipulation of architectural features of such polymer therapeutics. Garnering a detailed understanding of the various mechanisms by which multivalent polymers engage biological targets is certain to expand the role of polymers as therapeutics, by enabling highly specific activities of designed polymers in the biological environment.

Glycopeptide dendrimers, part III: a review. Use of glycopeptide dendrimers in immunotherapy and diagnosis of cancer and viral diseases

Glycopeptide dendrimers containing different types of tumor associated-carbohydrate antigens (T(N), TF, sialyl-T(N), sialyl-TF, sialyl-Le(x), sialyl-Le(a) etc.) were used in diagnosis and therapy of different sorts of cancer. These dendrimeric structures with incorporated T-cell epitopes and adjuvants can be used as antitumor vaccines. Best results were obtained with multiantigenic vaccines, containing, e.g. five or six different TAAs. The topic of TAAs and their dendrimeric forms at molecular level are reviewed, including structure, syntheses, and biological activities. Use of glycopeptide dendrimers as antiviral vaccines against HIV and influenza is also described. Their syntheses, physico-chemical properties, and biological activities are given with many examples.

Designing transient binding drugs: a new concept for drug discovery

A multitude of weak, or transient, biological interactions (dissociation constant: K(d)>microM), either working alone or in concert, occur frequently throughout biological systems. We are starting to appreciate their importance in complex biological networks. This realization has important implications to drug discovery as we can question the current paradigm of drug design to find the highest possible binders (drugs) to a given target (receptor). Development of transient drugs, defined by their binding to target, can be based on high-off-rates, multivalent approaches or multiple targets. Now, techniques are available to discover such drug candidates. The greatest problem yet to overcome is probably the mind-set of the individual researcher that weak binders are undesired and therefore of no benefit.

Carbohydrate receptors of bacterial adhesins: implications and reflections

Bacteria entering a host depend on adhesins to achieve colonization. Adhesins are bacterial surface structures mediating binding to host surficial areas. Most adhesins are composed of one or several proteins. Usually a single bacterial strain is able to express various adhesins. The adhesion type expressed may influence host-, tissue or even cell tropism of Gram-negative and of Gram-positive bacteria. The binding of fimbrial as well as of afimbrial adhesins of Gram-negative bacteria to host carbohydrate structures (=receptors) has been elucidated in great detail. In contrast, in Gram-positives, most well studied adhesins bind to proteinaceous partners. Nevertheless, for both bacterial groups the binding of bacterial adhesins to eukaryotic carbohydrate receptors is essential for establishing colonization or infection. The characterization of this interaction down to the submolecular level provides the basis for strategies to interfere with this early step of infection which should lead to the prevention of subsequent disease. However, this goal will not be achieved easily because bacterial adherence is not a monocausal event but rather mediated by a variety of adhesins.