Chondroitin Sulfate Tetrasaccharides: Synthesis, Three-Dimensional Structure and Interaction with Midkine

Chondroitin Sulfate-Coated Heteroduplex-Molecular Spherical Nucleic Acids

Molecular Spherical Nucleic Acids (MSNAs) are atomically uniform dendritic nanostructures and potential delivery vehicles for oligonucleotides. The radial formulation combined with covalent conjugation may hide the oligonucleotide content and simultaneously enhance the role of appropriate conjugate groups on the outer sphere. The conjugate halo may be modulated to affect the delivery properties of the MSNAs. In the present study, [60]fullerene-based molecular spherical nucleic acids, consisting of a 2'-deoxyribonucleotide and a ribonucleotide sequence, were used as hybridization-mediated carriers ("DNA and RNA-carriers") for an antisense oligonucleotide, suppressing Tau protein, (i. e. Tau-ASO) and its conjugates with chondroitin sulfate tetrasaccharides (CS) with different sulfation patterns. The impact of the MSNA carriers, CS-moieties on the conjugates and the CS-decorations on the MSNAs on cellular uptake and - activity (Tau-suppression) of the Tau-ASO was studied with hippocampal neurons in vitro. The formation and stability of these heteroduplex ASO-MSNAs were evaluated by UV melting profile analysis, polyacrylamide gel electrophoresis (PAGE), dynamic light scattering (DLS) and size exclusion chromatography equipped with a multi angle light scattering detector (SEC-MALS). The cellular uptake and - activity were studied by confocal microscopy and Western blot analysis, respectively.

Fluorescence polarization assays to study carbohydrate-protein interactions

Fluorescence polarization (FP) is a useful technique to study the interactions between carbohydrates and proteins in solution, by using standard equipment and minimal sample consumption. Here, we will review the most recent FP-based approaches in this field, including the study of carbohydrate-lectin, carbohydrate-enzyme and glycosaminoglycan-protein interactions. Advantages and limitations of this methodology will be discussed. To develop a FP procedure for studying carbohydrate-protein interactions, the main requirement is the design and synthesis of a suitable fluorescent glycan probe showing high affinity for the protein of interest. Different synthetic strategies employed for this purpose will be described, including the conjugation of 2-aminoethyl glycosides with amine-reactive fluorescein derivatives, the cycloaddition reaction between azido-functionalized saccharides and alkynylated fluorescent derivatives, and the reaction of the reducing end aldehyde group of an oligosaccharide with a hydrazide-containing fluorescein molecule. Competition FP experiments are particularly interesting because they enable the rapid screening of hundreds/thousands of non-labelled compounds for the discovery of molecules that block carbohydrate-protein binding, potentially modulating the subsequent biological processes.

Production of unsulfated chondroitin and associated chondro-oligosaccharides in recombinant Escherichia coli

We designed metabolically engineered non-pathogenic strains of Escherichia coli to produce unsulfated chondroitin with and without chondroitin lyase to produce the chondroitin polymer or its related oligosaccharides. Chondroitin was synthesized using chondroitin synthase KfoC and chondroitin was degraded using Pl35, a chondroitin lyase from Pedobacter heparinus. Pl35 behaved as a true endo-enzyme generating a large panel of oligosaccharides ranging from trimers to 18-mers instead of the di- and tetramers obtained with most chondroitin lyases. Two series of oligosaccharides were characterized, sharing an unsaturated uronic acid (4-deoxy-α-L-threo-hex-4-enepyranosyluronic acid, △UA) residue at their non-reducing end. The major "even-numbered" series was characterized by a terminal reducing N-acetylgalactosaminyl residue. The minor "odd-numbered" series oligosaccharides carried a terminal reducing glucuronic acid residue instead. Cultures were conducted in fed-batch conditions, and led to the production of up to 10 g L-1 chondroitin or chondroitin oligosaccharides. All products were purified and fully characterized using NMR and mass spectrometry analyses. This is the first report of the microbial production of large chondro-oligosaccharides.

Synthesis and interaction with growth factors of sulfated oligosaccharides containing an anomeric fluorinated tail

Compounds that mimic the biological properties of glycosaminoglycans (GAGs) and can be more easily prepared than the native GAG oligosaccharides are highly demanded. Here, we present the synthesis of sulfated oligosaccharides displaying a perfluorinated aliphatic tag at the reducing end as GAG mimetics. The preparation of these molecules was greatly facilitated by the presence of the fluorinated tail since the reaction intermediates were isolated by simple fluorous solid-phase extraction. Fluorescence polarization competition assays indicated that the synthesized oligosaccharides interacted with two heparin-binding growth factors, midkine (MK) and FGF-2, showing higher binding affinities than the natural oligosaccharides, and can be therefore considered as useful GAG mimetics. Moreover, NMR experiments showed that the 3D structure of these compounds is similar to that of the native sequences, in terms of sugar ring and glycosidic linkage conformations. Finally, we also demonstrated that these derivatives are able to block the MK-stimulating effect on NIH3T3 cells growth.

Nanoarchitectonics of cellulose nanocrystal conjugated with a tetrasaccharide-glycoprobe for targeting oligodendrocyte precursor cells

Demyelination is a serious complication of neurological disorders, which can be reversed by oligodendrocyte precursor cell (OPC) as the available source of myelination. Chondroitin sulfate (CS) plays key roles in neurological disorders, which still attracted less attention on how CS modulates the fate of OPCs. Nanoparticle coupled with glycoprobe is a potential strategy for investigating the carbohydrate-protein interaction. However, there is lack of CS-based glycoprobe with enough chain length that interact with protein effectively. Herein, we designed a responsive delivery system, in which CS was the target molecule, and cellulose nanocrystal (CNC) was the penetrative nanocarrier. A coumarin derivative (B) was conjugated at the reducing end of an unanimal-sourced chondroitin tetrasaccharide (4mer). This glycoprobe (4B) was grafted to the surface of a rod-like nanocarrier, which had a crystalline core and a poly(ethylene glycol) shell. This glycosylated nanoparticle (N4B-P) displayed a uniform size, improved water-solubility, and responsive release of glycoprobe. N4B-P displayed strong green fluorescence and good cell-compatibility, which imaged well the neural cells including astrocytes and OPCs. Interestingly, both of glycoprobe and N4B-P were internalized selectively by OPCs when they were incubated in astrocytes/OPCs mixtures. This rod-like nanoparticle would be a potential probe for studying carbohydrate-protein interaction in OPCs.

Sulfation of Heparan and Chondroitin Sulfate Ligands Enables Cell-Specific Homing of Nanoprobes

Demystifying the sulfation code of glycosaminoglycans (GAGs) to induce precise homing of nanoparticles in tumor cells or neurons influences the development of a potential drug- or gene-delivery system. However, GAGs, particularly heparan sulfate (HS) and chondroitin sulfate (CS), are structurally highly heterogeneous, and synthesizing well-defined HS/CS composed nanoparticles is challenging. Here, we decipher how specific sulfation patterns on HS and CS regulate receptor-mediated homing of nanoprobes in primary and secondary cells. We discovered that aggressive cancer cells such as MDA-MB-231 displayed a strong uptake of GAG-nanoprobes compared to mild or moderately aggressive cancer cells. However, there was no selectivity towards the GAG sequences, thus indicating the presence of more than one form of receptor-mediated uptake. However, U87 cells, olfactory bulb, and hippocampal primary neurons showed selective or preferential uptake of CS-E-coated nanoprobes compared to other GAG-nanoprobes. Furthermore, mechanistic studies revealed that the 4,6-O-disulfated-CS nanoprobe used the CD44 and caveolin-dependent endocytosis pathway for uptake. These results could lead to new opportunities to use GAG nanoprobes in nanomedicine.

Total synthesis of chondroitin sulfate E oligosaccharides and biological study

A total synthesis approach of CS-E oligosaccharides was established and a series of derivatives were synthesized. These oligosaccharides were evaluated for a glycosaminoglycan (GAG)-binding protein interaction against cytokines, midkine, and pleiotrophin, by surface-plasmon resonance (SPR) assay. The binding epitopes of oligosaccharides to midkine were mapped using a saturation transfer difference (STD) NMR technique. The groups on the reducing end contributed to binding affinity, and should not be ignored in biological assays. These findings contribute to the structure and activity relationship research and a foundation of understanding that will underpin potential future optimization of this class of oligosaccharides as pharmaceutical agents.

Design, Synthesis, and Evaluation of New Sugar-Substituted Imidazole Derivatives as Selective c-MYC Transcription Repressors Targeting the Promoter G-Quadruplex

c-MYC is a key driver of tumorigenesis. Repressing the transcription of c-MYC by stabilizing the G-quadruplex (G4) structure with small molecules is a potential strategy for cancer therapy. Herein, we designed and synthesized 49 new derivatives by introducing carbohydrates to our previously developed c-MYC G4 ligand 1. Among these compounds, 19a coupled with a d-glucose 1,2-orthoester displayed better c-MYC G4 binding, stabilization, and protein binding disruption abilities than 1. Our further evaluation indicated that 19a blocked c-MYC transcription by targeting the promoter G4, leading to c-MYC-dependent cancer cell death in triple-negative breast cancer cell MDA-MB-231. Also, 19a significantly inhibited tumor growth in the MDA-MB-231 mouse xenograft model accompanied by c-MYC downregulation. Notably, the safety of 19a was dramatically improved compared to 1. Our findings indicated that 19a could become a promising anticancer candidate, which suggested that introducing carbohydrates to improve the G4-targeting and antitumor activity is a feasible option.

Pleiotrophin Interaction with Synthetic Glycosaminoglycan Mimetics

Chondroitin sulfate (CS) E is the natural ligand for pleiotrophin (PTN) in the central nervous system (CNS) of the embryo. Some structures of PTN in solution have been solved, but no precise location of the binding site has been reported yet. Using ¹⁵N-labelled PTN and HSQC NMR experiments, we studied the interactions with a synthetic CS-E tetrasaccharide corresponding to the minimum binding sequence. The results agree with the data for larger GAG (glycosaminoglycans) sequences and confirm our hypothesis that a synthetic tetrasaccharide is long enough to fully interact with PTN. We hypothesize that the central region of PTN is an intrinsically disordered region (IDR) and could modify its properties upon binding. The second tetrasaccharide has two benzyl groups and shows similar effects on PTN. Finally, the last measured compound aggregated but beforehand, showed a behavior compatible with a slow exchange in the NMR time scale. We propose the same binding site and mode for the tetrasaccharides with and without benzyl groups.

The Interaction between Chondroitin Sulfate and Dermatan Sulfate Tetrasaccharides and Pleiotrophin

Pleiotrophin (PTN) is a neurotrophic factor that participates in the development of the embryonic central nervous system (CNS) and neural stem cell regulation by means of an interaction with sulfated glycosaminoglycans (GAGs). Chondroitin sulfate (CS) is the natural ligand in the CNS. We have previously studied the complexes between the tetrasaccharides used here and MK (Midkine) by ligand-observed NMR techniques. The present work describes the interactions between a tetrasaccharide library of synthetic models of CS-types and mimetics thereof with PTN using the same NMR transient techniques. We have concluded that: (1) global ligand structures do not change upon binding, (2) the introduction of lipophilic substituents in the structure of the ligand improves the strength of binding, (3) binding is weaker than for MK, (4) STD-NMR results are compatible with multiple binding modes, and (5) the replacement of GlcA for IdoA is not relevant for binding. Then we can conclude that the binding of CS derivatives to PTN and MK are similar and compatible with multiple binding modes of the same basic conformation.

Multigram scale preparation of a semi-synthetic N-trifluoroacetyl protected chondroitin disaccharide building block: Towards the stereoselective synthesis of chondroitin sulfates disaccharides

The chemoselective N-trifluoroacetylation of a chondroitin disaccharide obtained from controlled acid hydrolysis of a commercially available polymeric chondroitin sulfate is reported for the first time. We also described the multi-gram scale synthesis of a donor block having a benzylidene moiety further used for the expeditious and stereocontrolled synthesis of glycosides fitted with various aglycons. Stereocontrolled β-glycosylation, sulfation and efficient N-TFA deprotection steps afforded the desired disaccharides in good yields.

In-Depth Molecular Dynamics Study of All Possible Chondroitin Sulfate Disaccharides Reveals Key Insight into Structural Heterogeneity and Dynamism

GAGs exhibit a high level of conformational and configurational diversity, which remains untapped in terms of the recognition and modulation of proteins. Although GAGs are suggested to bind to more than 800 biologically important proteins, very few therapeutics have been designed or discovered so far. A key challenge is the inability to identify, understand and predict distinct topologies accessed by GAGs, which may help design novel protein-binding GAG sequences. Recent studies on chondroitin sulfate (CS), a key member of the GAG family, pinpointing its role in multiple biological functions led us to study the conformational dynamism of CS building blocks using molecular dynamics (MD). In the present study, we used the all-atom GLYCAM06 force field for the first time to explore the conformational space of all possible CS building blocks. Each of the 16 disaccharides was solvated in a TIP3P water box with an appropriate number of counter ions followed by equilibration and a production run. We analyzed the MD trajectories for torsional space, inter- and intra-molecular H-bonding, bridging water, conformational spread and energy landscapes. An in-house phi and psi probability density analysis showed that 1→3-linked sequences were more flexible than 1→4-linked sequences. More specifically, phi and psi regions for 1→4-linked sequences were held within a narrower range because of intra-molecular H-bonding between the GalNAc O5 atom and GlcA O3 atom, irrespective of sulfation pattern. In contrast, no such intra-molecular interaction arose for 1→3-linked sequences. Further, the stability of 1→4-linked sequences also arose from inter-molecular interactions involving bridged water molecules. The energy landscape for both classes of CS disaccharides demonstrated increased ruggedness as the level of sulfation increased. The results show that CS building blocks present distinct conformational dynamism that offers the high possibility of unique electrostatic surfaces for protein recognition. The fundamental results presented here will support the development of algorithms that help to design longer CS chains for protein recognition.

Total synthesis of the O-antigen repeating unit of Providencia stuartii O49 serotype through linear and one-pot assemblies

Capsular polysaccharides of pathogenic bacteria have been reported to be effective vaccines against diseases caused by them. Providencia stuartii is a class of enterobacteria of the family Providencia that is responsible for several antibiotic resistant infections, particularly urinary tract infections of patients with prolonged catheterization in hospital settings. Towards the goal of development of vaccine candidates against this pathogen, we herein report the total synthesis of a trisaccharide repeating unit of the O-antigen polysaccharide of the P. stuartii O49 serotype containing the →6)-β-ᴅ-Galp-(1→3)-β-ᴅ-GalpNAc(1→4)-α-ᴅ-Galp(1→ linkage. The synthesis of the trisaccharide repeating unit was carried out first by a linear strategy involving the [1 + (1 + 1 = 2)] assembly, followed by a one-pot synthesis involving [1 + 1 + 1] strategy from the corresponding monosaccharides. The one-pot method provided a higher yield of the protected trisaccharide intermediate (73%) compared to the two step synthesis (66%). The protected trisaccharide was then deprotected and N-acetylated to finally afford the desired trisaccharide repeating unit as its α-p-methoxyphenyl glycoside.

Midkine Interaction with Chondroitin Sulfate Model Synthetic Tetrasaccharides and Their Mimetics: The Role of Aromatic Interactions

Midkine (MK) is a neurotrophic factor that participates in the embryonic central nervous system (CNS) development and neural stem cell regulation, interacting with sulfated glycosaminoglycans (GAGs). Chondroitin sulfate (CS) is the natural ligand in the CNS. In this work, we describe the interactions between a library of synthetic models of CS-types and mimics. We did a structural study of this library by NMR and MD (Molecular Dynamics), concluding that the basic shape is controlled by similar geometry of the glycosidic linkages. Their 3D structures are a helix with four residues per turn, almost linear. We have studied the tetrasaccharide-midkine complexes by ligand observed NMR techniques and concluded that the shape of the ligands does not change upon binding. The ligand orientation into the complex is very variable. It is placed inside the central cavity of MK formed by the two structured beta-sheets domains linked by an intrinsically disordered region (IDR). Docking analysis confirmed the participation of aromatics residues from MK completed with electrostatic interactions. Finally, we test the biological activity by increasing the MK expression using CS tetrasaccharides and their capacity in enhancing the growth stimulation effect of MK in NIH3T3 cells.

Synthesis, self-assembly and Langerin recognition studies of a resorcinarene-based glycocluster exposing a hyaluronic acid thiodisaccharide mimetic

Herein, we report the synthesis of an octavalent glycocluster exposing a thiodisaccharide mimetic of the repetitive unit of hyaluronic acid, βSGlcA(1 → 3)βSGlcNAc, constructed on a calix[4]resorcinarene scaffold by CuAAC reaction of suitable precursors. This glycocluster showed a strong tendency toward self-aggregation. DOSY-NMR and DLS experiments demonstrated the formation of spherical micelles of d ≅ 6.2 nm, in good agreement. TEM micrographs showed the presence of particles of different sizes, depending on the pH of the starting solution, thus evidencing that the negative charge on the micelle surface due to ionization of the GlcA residues plays an important role in the aggregation process. STD-NMR and DLS experiments provided evidence of the interaction between the synthetic glycocluster and Langerin, a relevant C-type lectin. This interaction was not observed in the STD-NMR experiments performed with the basic disaccharide, providing evidence of a multivalent effect.

Synthesis, structure and midkine binding of chondroitin sulfate oligosaccharide analogues

The preparation of chondroitin sulfate (CS) oligosaccharide mimetics, more easily synthesized than natural sequences, is a highly interesting task because these compounds pave the way for modulation of the biological processes in which CS is involved. Herein, we report the synthesis of CS type E analogues which present easily accessible glucose units instead of glucuronic acid (GlcA) moieties. NMR experiments and molecular dynamics simulations showed that the 3D structure of these compounds is similar to the structure of the natural CS-E oligosaccharides. In addition, fluorescence polarization (FP) and saturation transfer difference NMR (STD-NMR) experiments revealed that the synthesized CS-like derivatives were able to interact with midkine, a model heparin-binding growth factor, suggesting that the presence of the GlcA carboxylate groups is not essential for the binding. Overall, our results indicate that the synthesized glucose-containing oligosaccharides can be considered as functional and structural CS mimetics.

NMR Characterization of the Interactions Between Glycosaminoglycans and Proteins

Glycosaminoglycans (GAGs) constitute a considerable fraction of the glycoconjugates found on cellular membranes and in the extracellular matrix of virtually all mammalian tissues. The essential role of GAG-protein interactions in the regulation of physiological processes has been recognized for decades. However, the underlying molecular basis of these interactions has only emerged since 1990s. The binding specificity of GAGs is encoded in their primary structures, but ultimately depends on how their functional groups are presented to a protein in the three-dimensional space. This review focuses on the application of NMR spectroscopy on the characterization of the GAG-protein interactions. Examples of interpretation of the complex mechanism and characterization of structural motifs involved in the GAG-protein interactions are given. Selected families of GAG-binding proteins investigated using NMR are also described.

Pleiotrophin interacts with glycosaminoglycans in a highly flexible and adaptable manner

Pleiotrophin (PTN) is a potent mitogenic cytokine whose activities are controlled by its interactions with glycosaminoglycan (GAG). We examined the specificity of PTN for several types of GAG oligosaccharides. Our data indicate that the interaction of PTN with GAGs is dependent on the sulfation density of GAGs. Surprisingly, an acidic peptide also had similar interactions with PTN as GAGs. This shows that the interaction of PTN with anionic polymers is flexible and adaptable and that the charge density is the main determinant of the interaction. In addition, we show that PTN can compensate for the loss of its termini in interactions with heparin oligosaccharides, allowing it to maintain its affinity for GAGs in the absence of the termini. Taken together, these data provide valuable insight into the interactions of PTN with its proteoglycan receptors.

Glycosaminoglycans in Neurodegenerative Diseases

Glycosaminoglycans (GAGs) are linear polysaccharides that consist of alternating disaccharides sequences of uronic acids and/or galactose hexamino sugars most of which are sulfated. GAGs are ubiquitously expressed on the cell surface, in the intracellular milieu and in the extracellular matrix of all animal cells. Thus, GAGs exhibit many essential roles in a variety of physiological and pathological processes. The targets of GAGs are GAG-binding proteins and related proteins that are of significant interest to both the academic community and in the pharmaceutical industry. In this review, the structures of GAGs, their binding proteins, and analogs are presented that further the development of GAGs and their analogs for the treatment of neurodegenerative diseases agents.

Chemical Synthesis of Fucosylated Chondroitin Sulfate Oligosaccharides

Fucosylated chondroitin sulfates (FuCSs) are a unique type of polysaccharides occurring in sea cucumber that show a variety of biological activities. In particular, well-defined FuCS oligosaccharides, consisting of a trisaccharide repeating unit of β-d-GalNAc(4,6-diS)-(1→4)-[α-l-Fuc(2,4-diS)-(1→3)]-β-d-GlcUA, display potent anticoagulant activity via selective inhibition of the intrinsic tenase, which could be developed into anticoagulant drugs without bleeding risk. Herein, we report an effective approach to the synthesis of FuCS oligosaccharides, as demonstrated by the successful elaboration of FuCS tri-, hexa-, and nonasaccharides. The syntheses employ an orthogonally protected trisaccharide as a pivotal building block that can be readily converted into the donor and acceptor for glycosidic coupling. In addition, the internal patterns of protecting groups, involving N-trichloroacetyl for N-acetyl group, benzylidene and benzyl groups for sulfonated hydroxyl groups, and benzoyl and methyl esters for free hydroxyl and carboxylic acid, respectively, ensure stereoselective formation of the glycosidic linkages and sequential transformation into the desired FuCS oligosaccharides.

Aggrecan, the Primary Weight-Bearing Cartilage Proteoglycan, Has Context-Dependent, Cell-Directive Properties in Embryonic Development and Neurogenesis: Aggrecan Glycan Side Chain Modifications Convey Interactive Biodiversity

This review examines aggrecan's roles in developmental embryonic tissues, in tissues undergoing morphogenetic transition and in mature weight-bearing tissues. Aggrecan is a remarkably versatile and capable proteoglycan (PG) with diverse tissue context-dependent functional attributes beyond its established role as a weight-bearing PG. The aggrecan core protein provides a template which can be variably decorated with a number of glycosaminoglycan (GAG) side chains including keratan sulphate (KS), human natural killer trisaccharide (HNK-1) and chondroitin sulphate (CS). These convey unique tissue-specific functional properties in water imbibition, space-filling, matrix stabilisation or embryonic cellular regulation. Aggrecan also interacts with morphogens and growth factors directing tissue morphogenesis, remodelling and metaplasia. HNK-1 aggrecan glycoforms direct neural crest cell migration in embryonic development and is neuroprotective in perineuronal nets in the brain. The ability of the aggrecan core protein to assemble CS and KS chains at high density equips cartilage aggrecan with its well-known water-imbibing and weight-bearing properties. The importance of specific arrangements of GAG chains on aggrecan in all its forms is also a primary morphogenetic functional determinant providing aggrecan with unique tissue context dependent regulatory properties. The versatility displayed by aggrecan in biodiverse contexts is a function of its GAG side chains.

Saturation Transfer Difference in Characterization of Glycosaminoglycan-Protein Interactions

Novel methods in nuclear magnetic resonance (NMR) spectroscopy have recently been developed to investigate the binding properties of intermolecular complexes endowed with biomedical functions. Among these methods is the saturation transfer difference (STD), which enables the mapping of specific binding motifs of functional ligands. STD can efficiently uncover the specific and preferential binding sites of these ligands in their intermolecular complexes. This is particularly useful in the case of glycosaminoglycans (GAGs), a group of sulfated polysaccharides that play pivotal roles in various biological and pathological processes. The activity of GAGs is ultimately mediated through molecular interactions with key functional proteins, namely, GAG-binding proteins (GBPs). The quality of the GAG-GBP interactions depends on sulfation patterns, oligosaccharide length, and the composing monosaccharides of GAGs. Through STD NMR, information about the atoms of the GAG ligands involved in the complexes is provided. Here we highlight the latest achievements of the literature using STD NMR on GAG oligosaccharide-GBP complexes. Interestingly, most of the GBPs studied so far by STD NMR belong to one of the three major classes: coagulation factors, growth factors, or chemokine/cytokines. Unveiling the structural requirements of GAG ligands in bindings with their protein partners is a crucial step to understand the biochemical and medical actions of GAGs. This process is also a requirement in GAG-based drug discovery and development.

Influence of the reducing-end anomeric configuration of the Man9 epitope on DC-SIGN recognition

The anomeric configuration of the reducing end of Man₉ does not influence the binding to DC-SIGN.

Preparation, Characterization, and Inhibition of Hyaluronic Acid Oligosaccharides in Triple-Negative Breast Cancer

Hyaluronic acid (hyaluronan, HA) is a critical component of the extracellular matrix and plays an important biological function of interacting with different molecules and receptors. In this study, both odd- and even-numbered HA oligosaccharides (HAOs) with specific degrees of polymerization (DP) were prepared by different hydrochloric acid hydrolyses, and their structures were characterized by means of HPLC, ESI-MS, and NMR. The data show that the odd-numbered HAOs (DP3-11) have a glucuronic acid reducing end, while the even-numbered HAOs (DP2-10) have an N-acetylglucosamine reducing end. Biological evaluations indicated that all HAOs significantly inhibited the growth and migration of triple-negative breast cancer (TNBC) MDA-MB-231 cells. Among these oligosaccharides, the HA tetrasaccharide (DP4) was confirmed to be the minimum fragment necessary to inhibit MDA-MB-231 cells. Our data suggest that HAOs have potential value in the treatment of TNBC.

The synthesis and biological evaluation of chondroitin sulfate E glycodendrimers

Aim: Chondroitin sulfate (CS) is a class of highly sulfated polysaccharides that possess many important biological functions. The heterogeneity of CS limits pharmacological research and leads to ambiguous mechanisms. Thus, glycomimetics are demanded as replacement of natural polysaccharides to explore important biological processes. Results & methodology: Here the preparation of CS glycodendrimers is reported as well as their use as CS mimetics to regulate the NF-κB pathway. Multivalent presentation of sugar epitopes on appropriate dendrimer scaffolds increased the suppression of the NF-κB pathway. The interaction between CS-E molecules and TNF-α was examined by nuclear magnetic resonance technology. Conclusion: Overall, the glycodendrimer reported here may be potentially employed as molecular tool to investigate the biological functions of CS.

Synthesis of a Fluorous-Tagged Hexasaccharide and Interaction with Growth Factors Using Sugar-Coated Microplates

Here, we report the synthesis of a sulfated, fully protected hexasaccharide as a glycosaminoglycan mimetic and the study of its interactions with different growth factors: midkine, basic fibroblast growth factor (FGF-2) and nerve growth factor (NGF). Following a fluorous-assisted approach, monosaccharide building blocks were successfully assembled and the target oligosaccharide was prepared in excellent yield. The use of more acid stable 4,6-O-silylidene protected glucosamine units was crucial for the efficiency of this strategy because harsh reaction conditions were needed in the glycosylations to avoid the formation of orthoester side products. Fluorescence polarization experiments demonstrated the strong interactions between the synthesized hexamer, and midkine and FGF-2. In addition, we have developed an alternative assay to analyse these molecular recognition events. The prepared oligosaccharide was non-covalently attached to a fluorous-functionalized microplate and the direct binding of the protein to the sugar-immobilized surface was measured, affording the corresponding K_D,surf value.

Unexpected loss of stereoselectivity in glycosylation reactions during the synthesis of chondroitin sulfate oligosaccharides

Here, we present an exploratory study on the fluorous-assisted synthesis of chondroitin sulfate (CS) oligosaccharides. Following this approach, a CS tetrasaccharide was prepared. However, in contrast to our previous results, a significant loss of β-selectivity was observed in [2 + 2] glycosylations involving N-trifluoroacetyl-protected D-galactosamine donors and D-glucuronic acid (GlcA) acceptors. These results, together with those obtained from experiments employing model monosaccharide building blocks, highlight the impact of the glycosyl acceptor structure on the stereoselectivity of glycosylation reactions. Our study provides useful data about the substitution pattern of GlcA units for the efficient synthesis of CS oligomers.

Synthesis of Azide-Modified Chondroitin Sulfate Precursors: Substrates for "Click"- Conjugation with Fluorescent Labels and Oligonucleotides

Azidopropyl-modified precursors of chondroitin sulfate (CS) tetrasaccharides have been synthesized, which, after facile conversion to final CS structures, may be conjugated with alkyne-modified target compounds by a one-pot “click”-ligation. RP HPLC was used for the monitoring of the key reaction steps (protecting group manipulation and sulfation) and purification of the CS precursors (as partially protected form, bearing the O-Lev, O-benzoyl, and N-trichloroacetyl groups and methyl esters). Subsequent treatments with aqueous NaOH, concentrated ammonia, and acetic anhydride (i.e., global deprotection and acetylation of the galactosamine units) converted the precursors to final CS structures. The azidopropyl group was exposed to a strain-promoted azide–alkyne cycloaddition (SPAAC) with a dibenzylcyclooctyne-modified carboxyrhodamine dye to give labeled CSs. Conjugation with a 5′-cyclooctyne-modified oligonucleotide was additionally carried out to show the applicability of the precursors for the synthesis of biomolecular hybrids.

An Approach to Synthesize Chondroitin Sulfate-E (CS-E) Oligosaccharide Precursors

An approach was developed to synthesize chondroitin sulfate-E (CS-E) oligosaccharides by adopting a postglycosylation-transformation strategy: different from all of the traditional approaches, the characteristic groups of CS-E were introduced following the assembly of the oligosaccharides. The adjusted strategy rendered an easy chain elongation strategy. All of the elongation steps generated high yields with excellent glycosylation outcomes. An orthogonally protected disaccharide was used as the building block to provide flexibility for the group transformation and derivatization at the N-2 position of the GalNAc residue and the O-1,5 positions of the GlcA residue, thereby providing ready access for the further examination of the structure-activity relationship (SAR) of CS-E molecules.

Enzymatic Synthesis of Homogeneous Chondroitin Sulfate Oligosaccharides

Chondroitin sulfate (CS) is a sulfated polysaccharide that plays essential physiological roles. Here, we report an enzyme-based method for the synthesis of a library of 15 different CS oligosaccharides. This library covers 4-O-sulfated and 6-O-sulfated oligosaccharides ranging from trisaccharides to nonasaccharides. We also describe the synthesis of unnatural 6-O-sulfated CS pentasaccharides containing either a 6-O-sulfo-2-azidogalactosamine or a 6-O-sulfogalactosamine residue. The availability of structurally defined CS oligosaccharides offers a novel approach to investigate the biological functions of CS.

Chondroitin sulfates and their binding molecules in the central nervous system

Chondroitin sulfate (CS) is the most abundant glycosaminoglycan (GAG) in the central nervous system (CNS) matrix. Its sulfation and epimerization patterns give rise to different forms of CS, which enables it to interact specifically and with a significant affinity with various signalling molecules in the matrix including growth factors, receptors and guidance molecules. These interactions control numerous biological and pathological processes, during development and in adulthood. In this review, we describe the specific interactions of different families of proteins involved in various physiological and cognitive mechanisms with CSs in CNS matrix. A better understanding of these interactions could promote a development of inhibitors to treat neurodegenerative diseases.

Effects of Ethanol on Brain Extracellular Matrix: Implications for Alcohol Use Disorder

The brain extracellular matrix (ECM) occupies the space between cells and is involved in cell-matrix and cell-cell adhesion. However, in addition to providing structural support to brain tissue, the ECM activates cell signaling and controls synaptic transmission. The expression and activity of brain ECM components are regulated by alcohol exposure. This review will discuss what is currently known about the effects of alcohol on the activity and expression of brain ECM components. An interpretation of how these changes might promote alcohol use disorder (AUD) will be also provided. Ethanol (EtOH) exposure decreases levels of structural proteins involved in the interstitial matrix and basement membrane, with a concomitant increase in proteolytic enzymes that degrade these components. In contrast, EtOH exposure generally increases perineuronal net components. Because the ECM has been shown to regulate both synaptic plasticity and behavioral responses to drugs of abuse, regulation of the brain ECM by alcohol may be relevant to the development of alcoholism. Although investigation of the function of brain ECM in alcohol abuse is still in early stages, a greater understanding of the interplay between ECM and alcohol might lead to novel therapeutic strategies for treating AUD.

Efficient and stereocontrolled synthesis of chondroitin mono- and disaccharide linked to variously sulfated biotinylated trisaccharides of the linkage region of proteoglycans

Efficient and stereocontrolled preparation of a library of variously sulfated biotinylated tetra- and pentasaccharides possessing the backbone of the partial linkage region plus the first chondroitin sulfate mono- or disaccharide unit (d-GlcA)n-β-d-(1,3)-GalNAc-β-d-(1,4)-GlcA-β-d-(1,3)-Gal-β-d-(1,3)-Gal (n = 0 or 1) is reported herein for the first time. The synthesis of these compounds was achieved using common key intermediates and a disaccharide building block obtained by semisynthesis. Stereoselective glycosylation, selective protection/deprotection steps, efficient reduction of the N-trichloroacetyl group into the corresponding N-acetyl group, efficient sulfation strategy, deprotection and biotinylation afforded target oligomers in good yield with high purity.

Role of Chondroitin Sulfate (CS) Modification in the Regulation of Protein-tyrosine Phosphatase Receptor Type Z (PTPRZ) Activity: PLEIOTROPHIN-PTPRZ-A SIGNALING IS INVOLVED IN OLIGODENDROCYTE DIFFERENTIATION

Protein-tyrosine phosphatase receptor type Z (PTPRZ) is predominantly expressed in the developing brain as a CS proteoglycan. PTPRZ has long (PTPRZ-A) and short type (PTPRZ-B) receptor forms by alternative splicing. The extracellular CS moiety of PTPRZ is required for high-affinity binding to inhibitory ligands, such as pleiotrophin (PTN), midkine, and interleukin-34; however, its functional significance in regulating PTPRZ activity remains obscure. We herein found that protein expression of CS-modified PTPRZ-A began earlier, peaking at approximately postnatal days 5-10 (P5-P10), and then that of PTN peaked at P10 at the developmental stage corresponding to myelination onset in the mouse brain. Ptn-deficient mice consistently showed a later onset of the expression of myelin basic protein, a major component of the myelin sheath, than wild-type mice. Upon ligand application, PTPRZ-A/B in cultured oligodendrocyte precursor cells exhibited punctate localization on the cell surface instead of diffuse distribution, causing the inactivation of PTPRZ and oligodendrocyte differentiation. The same effect was observed with the removal of CS chains with chondroitinase ABC but not polyclonal antibodies against the extracellular domain of PTPRZ. These results indicate that the negatively charged CS moiety prevents PTPRZ from spontaneously clustering and that the positively charged ligand PTN induces PTPRZ clustering, potentially by neutralizing electrostatic repulsion between CS chains. Taken altogether, these data indicate that PTN-PTPRZ-A signaling controls the timing of oligodendrocyte precursor cell differentiation in vivo, in which the CS moiety of PTPRZ receptors maintains them in a monomeric active state until its ligand binding.

Improvement on binding of chondroitin sulfate derivatives to midkine by increasing hydrophobicity

The relative binding affinities of sulfated, fully protected chondroitin sulfate oligosaccharides for midkine are much higher than those displayed by the natural deprotected sequences.