Synthesis of ganglioside epitopes for oligosaccharide specific immunoadsorption therapy of Guillian-Barré syndrome

Design, Synthesis and Antiparasitic Evaluation of Click Phospholipids

A library of seventeen novel ether phospholipid analogues, containing 5-membered heterocyclic rings (1,2,3-triazolyl, isoxazolyl, 1,3,4-oxadiazolyl and 1,2,4-oxadiazolyl) in the lipid portion were designed and synthesized aiming to identify optimised miltefosine analogues. The compounds were evaluated for their in vitro antiparasitic activity against Leishmania infantum and Leishmania donovani intracellular amastigotes, against Trypanosoma brucei brucei and against different developmental stages of Trypanosoma cruzi. The nature of the substituents of the heterocyclic ring (tail) and the oligomethylene spacer between the head group and the heterocyclic ring was found to affect the activity and toxicity of these compounds leading to a significantly improved understanding of their structure-activity relationships. The early ADMET profile of the new derivatives did not reveal major liabilities for the potent compounds. The 1,2,3-triazole derivative 27 substituted by a decyl tail, an undecyl spacer and a choline head group exhibited broad spectrum antiparasitic activity. It possessed low micromolar activity against the intracellular amastigotes of two L. infantum strains and T. cruzi Y strain epimastigotes, intracellular amastigotes and trypomastigotes, while its cytotoxicity concentration (CC50) against THP-1 macrophages ranged between 50 and 100 μM. Altogether, our work paves the way for the development of improved ether phospholipid derivatives to control neglected tropical diseases.

Oligosaccharide Antigen Conjugation to Carrier Proteins to Formulate Glycoconjugate Vaccines

Conjugation, that is, covalent linkage, to immunological proteins is a common strategy to address the low immunogenicity issue of carbohydrate antigens in vaccine development. This chapter describes an easy and efficient method for oligosaccharide-protein conjugation employing dicarboxylic acid linkers. In this regard, a free amino group is introduced to an oligosaccharide antigen to facilitate coupling with the bifunctional linker upon reaction with its corresponding disuccinimidyl ester. The resultant monosuccinimidyl ester of the oligosaccharide antigen then reacts with the free amino groups of a carrier protein to provide the desired oligosaccharide-protein conjugate.

Synthesis of neuraminidase-resistant sialoside-modified three-way junction DNA and its binding ability to various influenza viruses

Natural sialic acid-modified compounds are capable of targeting influenza virus hemagglutinin (HA). However, these compounds have limited inhibitory effect because natural O-glycoside bond in these compounds are prone to be cleaved by neuraminidase (NA) on the surface of viruses. In this study, we synthesized NA-resistant sialoside that included unnatural S-glycoside bonds and modified this sialoside on a three-way junction (3WJ) DNA to display complementary distribution to its binding sites on a HA trimer. This S-glycoside-containing sialoside-modified 3WJ DNA showed certain NA resistance and maintained high binding affinity. Importantly, our observations showed that substituting natural O-glycoside with unnatural S-glycoside did not affect the binding affinity of the sialoside-modified 3WJ DNA for viruses. Thus, this study is an important step forward in the development of NA-resistant sialoside derivatives for more effective detection and inhibition of infection by a broad spectrum of viruses.

Synthesis of rationally designed tetrasaccharides for crystallographic and binding studies with Clostridium difficile toxins and unexpected partial N-methylations during catalytic hydrogenation of azides in methanol

A β-GlcNAc-LeX tetrasaccharides and another α-Gal-LeX analog have been synthesized for studying interaction with toxins produced by the human pathogen Clostridium difficile. LeX-based trisaccharides bearing either a 2-azidoethyl or a 6-azidohexyl aglycone have been employed in the total synthesis to afford the desired tetrasaccharides. Interestingly, during the final catalytic hydrogenation step to remove benzyl and benzylidene protecting groups and simultaneously reduce azide functionality, partial N-methylations were observed. The N-methylations appear to be a general issue with catalytic hydrogenation of azides in methanol.

Organic modification and subsequent biofunctionalization of porous anodic alumina using terminal alkynes

Porous anodic alumina (PAA) is a well-defined material that has found many applications. The range of applications toward sensing and recognition can be greatly expanded if the alumina surface is covalently modified with an organic monolayer. Here, we present a new method for the organic modification of PAA based on the reaction of terminal alkynes with the alumina surface. The reaction results in the the formation of a monolayer within several hours at 80 °C and is dependent on both oxygen and light. Characterization with X-ray photoelectron spectroscopy and infrared spectroscopy indicates formation of a well-defined monolayer in which the adsorbed species is an oxidation product of the 1-alkyne, namely, its α-hydroxy carboxylate. The obtained monolayers are fairly stable in water and at elevated temperatures, as was shown by monitoring the water contact angle. Modification with 1,15-hexadecadiyne resulted in a surface that has alkyne end groups available for further reaction, as was demonstrated by the subsequent reaction of N-(11-azido-3,6,9-trioxaundecyl)trifluoroacetamide with the modified surface. Biofunctionalization was explored by coupling 11-azidoundecyl lactoside to the surface and studying the subsequent adsorption of the lectin peanut agglutinin (PNA) and the yeast Candida albicans, respectively. Selective and reversible binding of PNA to the lactosylated surfaces was demonstrated. Moreover, PNA adsorption was higher on surfaces that exposed the β-lactoside than on those that displayed the α anomer, which was attributed to surface-associated steric hindrance. Likewise, the lactosylated surfaces showed increased colonization of C. albicans compared to unmodified surfaces, presumably due to interactions involving the cell wall β-glucan. Thus, this study provides a new modification method for PAA surfaces and shows that it can be used to induce selective adsorption of proteins and microorganisms.

Pathogenesis and treatment of immune-mediated neuropathies

Immune-mediated neuropathies represent a heterogeneous spectrum of peripheral nerve disorders that can be classified according to time course, predominant involvement of motor/sensory fibers, distribution of deficits and paraclinical parameters such as electrophysiology and serum antibodies. In the last few years, significant advances have been achieved in elucidating underlying pathomechanisms, which made it possible to identify potential therapeutic targets. In this review, we discuss the latest development in pathogenesis and treatment of immune-mediated neuropathies.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2003-2004

This review is the third update of the original review, published in 1999, on the application of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings the topic to the end of 2004. Both fundamental studies and applications are covered. The main topics include methodological developments, matrices, fragmentation of carbohydrates and applications to large polymeric carbohydrates from plants, glycans from glycoproteins and those from various glycolipids. Other topics include the use of MALDI MS to study enzymes related to carbohydrate biosynthesis and degradation, its use in industrial processes, particularly biopharmaceuticals and its use to monitor products of chemical synthesis where glycodendrimers and carbohydrate-protein complexes are highlighted.

Anti-ganglioside antibodies and the presynaptic motor nerve terminal

The Guillain Barré syndromes (GBS) are the world's leading cause of acute autoimmune neuromuscular paralysis. Understanding the pathophysiological events of GBS, and improving immunotherapies are fundamental to improving the clinical outcome. Recent research into GBS and the Miller Fisher syndrome (MFS) variant has focused on the forms mediated by anti-ganglioside antibodies in which correlations have been established between anti-ganglioside antibodies and specific clinical phenotypes, notably between anti-GM1/GD1a antibodies and the acute motor axonal variant and anti-GQ1b/GT1a antibodies and MFS. Anti-ganglioside antibodies can arise through molecular mimicry with GBS-associated Campylobacter jejuni oligosaccharides. Our work has focused on axonal and glial components of the motor nerve terminal as a model site of injury, and through combined active and passive immunization paradigms in glycosyltransferase knockout mice we have developed murine neuropathy phenotypes mediated by anti-ganglioside antibodies. Several determinants influence disease expression including the level of immunological tolerance to microbial glycans that mimic self gangliosides, the degree of complement activation, and the ganglioside density in target tissue. Such studies provide us with clear information on an antibody-mediated pathogenesis model for GBS and should lead to rational therapeutic testing of agents that are potentially suitable for use in man.

Preparation of carbohydrate-oligonucleotide conjugates using the squarate spacer

Attachment of carbohydrates to oligonucleotides has proven to induce receptor-mediated endocytosis. A facile method for the formation of covalent linkages between glycans and oligonucleotides is herein described. Thus, use of 3,4-diethoxy-3-cyclobutene-1,2-dione as a linking reagent provides easy conjugation between carbohydrates bearing an amino group at the reducing end and oligonucleotides bearing an aminoalkyl modification.

Gangliosides as targets for autoimmune injury to the nervous system

Immune responses directed towards gangliosides and their microbial mimics are important mediators of several subtypes of acute post-infectious autoimmune neuropathy, collectively referred to as the Guillain-Barré syndromes. In this diverse group of paralytic syndromes, the immunopathology is in a proportion of cases characterised by anti-ganglioside antibody deposits, accompanied by inflammatory destruction of both axonal and glial components within the PNS. By gaining an understanding of the immunological mechanisms underlying these pathological pathways, it should be possible to select the correct targets for therapeutic intervention. Recent years has seen particular progress in our understanding of the basis for, and immunological consequences of molecular mimicry between gangliosides and microbial glycans, the relationships between ganglioside antibody specificity and different clinical phenotypes of GBS, the pathological basis for antibody-mediated nerve injury and the testing of intervention strategies in pre-clinical models. The focus of this mini-review is to provide a brief background to this field, summarise a selection of recent highlights focused on our own research, identify areas of outstanding knowledge and present data that supports novel therapeutic approaches based on the latest experimental findings.

Syntheses of Lewis(x) and dimeric Lewis(x): construction of branched oligosaccharides by a combination of preactivation and reactivity based chemoselective one-pot glycosylations

Two asymmetrically branched oligosaccharides, LewisX and dimeric LewisX, were assembled in one pot with high yields and exclusive regio- and stereoselectivities. p-Tolyl thioglycosides were utilized as the sole type of building blocks, thus simplifying the overall synthetic design. The reactivity-independent nature of the preactivation based method allows modular assembly of the dimeric LewisX octasaccharide without the need for tedious protective group manipulation to achieve exact anomeric reactivities.

Solid phase immunoadsorption for therapeutic and analytical studies on neuropathy-associated anti-GM1 antibodies

Autoimmune neuropathies including Guillain-Barré syndrome are frequently associated with anti-GM1 ganglioside antibodies. These are believed to play a pathogenic role and their clearance from the circulation would be predicted to produce therapeutic benefit. This study examines the conditions required for effective immunoadsorption of anti-GM1 antibodies using glycan-conjugated Sepharose as a matrix. In solution inhibition studies using a range of GM1-like saccharides in conjunction with mouse and human anti-GM1 antibodies, the whole GM1 pentasaccharide beta-Gal-(1-3)-beta-GalNAc-(1-4)-[alpha-Neu5Ac-(2-3)]-beta-Gal-(1-4)-beta-Glc was the favored ligand for maximal inhibiton of antibody-GM1 interactions in comparison with monosaccharides, Gal-(1-3)-beta-GalNAc-betaOMe, and synthetic GM1 mimetics. Immunoadsorption studies comparing binding of mouse monoclonal anti-GM1 antibodies to GM1-Sepharose and beta-Gal-(1-3)-beta-GalNAc-Sepharose confirmed the preference seen in solution inhibition studies. GM1-Sepharose columns were then used to adsorb anti-GM1 immunoglobulin G and immunoglobulin M antibodies from human neuropathy sera. Anti-GM1 antibodies subsequently eluted from the columns often showed a striking monoclonal or oligoclonal pattern, indicating that the immune response to GM1 is restricted to a limited number of B-cell clones, even in the absence of a detectable serum paraprotein. These data support the view that immunoadsorption plasmapheresis could potentially be developed for the acute depletion of serum anti-GM1 antibodies in patients with neuropathic disease, and also provide purified human anti-GM1 antibodies for analytical studies.

Synthesis of glycoconjugate vaccines for Candida albicans using novel linker methodology

[reaction: see text] The cell wall phosphomannan of Candida species is a complex N-linked glycoprotein with a glycan chain that contains predominantly alpha-linked mannose residues. However, it is the minor beta-mannan component of the phosphomannan of clinically important Candida strains that provides immunological protection in animal models of fungal disease and hence holds promise as a component of conjugate vaccines. This important antigen occurs in different forms linked to the alpha-mannan backbone via a phosphodiester bond (acid-labile beta-mannan) or directly via a glycosidic bond. To reproducibly synthesize and evaluate conjugate vaccines, a robust method for the synthesis of the different oligosaccharide epitopes is required. Here, we report the gram-scale syntheses of both types of epitopes by an approach that utilizes glucosyl trichloroacetimidate donor 2 to first create a beta-glucopyranoside linkage and then epimerizes the C-2 center via an oxidation-reduction sequence that provides an efficient multigram scale route to the beta-mannopyranosides 5, 8, and 15. Reaction of glycosides 16-18 with homobifunctional adipic acid p-nitrophenyl diesters in dry DMF gave the corresponding half esters in good yields, and of sufficient stability to permit chromatographic purification. Subsequent conjugation with BSA and tetanus toxiod (TT) under mild conjugation conditions afforded the corresponding tri- and tetrasaccharide neoglycoproteins with good efficiency. The conjugation method is also applicable to the coupling of small amounts (mg) of larger oligosaccharides with different proteins.

Synthesis of mono- and di-sialophospholipids via the H-phosphonate approach

To overcome their inherent instability, stable modified mono- and di-sialophospholipids of the group C meningococcal polysaccharide were synthesized. Stability was achieved by introducing a spacer between the sialic acid residue and the phospholipid component, and by replacing the native ester linkages to the lipid by ether linkages. Mono- and di-hydroxylethylenesialosides were coupled to phosphoglyceroldietherlipid using H-phosphonate chemistry to give the anomerically pure sialophospholipids in good yields.Key words: polysialic acid, glycolipid, H-phosphonate, meningococcus.

Anti-disialosyl antibodies mediate selective neuronal or Schwann cell injury at mouse neuromuscular junctions

The human paralytic neuropathy, Miller Fisher syndrome (MFS) is associated with autoantibodies specific for disialosyl epitopes on gangliosides GQ1b, GT1a, and GD3. Since these gangliosides are enriched in synaptic membranes, anti-ganglioside antibodies may target neuromuscular junctions (NMJs), thereby contributing to disease symptoms. We have shown previously that at murine NMJs, anti-disialosyl antibodies induce an alpha-latrotoxin-like effect, electrophysiologically characterized by transient massive increase of spontaneous neurotransmitter release followed by block of evoked release, resulting in paralysis of the muscle preparation. Morphologically, motor nerve terminal damage, as well as perisynaptic Schwann cell (pSC) death is observed. The relative contributions of neuronal and pSC injury to the paralytic effect and subsequent repair are unknown. In this study, we have examined the ability of subsets of anti-disialosyl antibodies to discriminate between the neuronal and glial elements of the NMJ and thereby induce either neuronal injury or pSC death. Most antibodies reactive with GD3 induced pSC death, whereas antibody reactivity with GT1a correlated with the extent of nerve terminal injury. Motor nerve terminal injury resulted in massive uncontrolled exocytosis with paralysis. However, pSC ablation induced no acute (within 1 h) electrophysiological or morphological changes to the underlying nerve terminal. These data suggest that at mammalian NMJs, acute pSC injury or ablation has no major deleterious influence on synapse function. Our studies provide evidence for highly selective targeting of mammalian NMJ membranes, based on ganglioside composition, that can be exploited for examining axonal-glial interactions both in disease states and in normal NMJ homeostasis.

Chemoenzymatic synthesis of GM3and GM2gangliosides containing a truncated ceramide functionalized for glycoconjugate synthesis and solid phase applications

Analogues of GM3 and GM2 gangliosides were chemoenzymatically synthesized on a multifunctional ceramide-type tether designed to facilitate diverse strategies for glycoconjugate synthesis. The truncated ceramide aglycon maintains the stereogenic centres of natural ceramide while avoiding extensive hydrophobicity that can hamper synthesis and purification of the glycolipids. Tetanus toxoid and BSA glycoconjugates of these two gangliosides were prepared for immunization of mice, and for solid phase assays to screen for ganglioside-specific antibodies. Inhibition experiments showed that antibodies generated by tetanus toxoid conjugates of GM3 and GM2 exhibited specificity for the carbohydrate epitope and the stereogenic centres of the ceramide.

The immunobiology of Guillain-Barré syndromes

This presentation highlights aspects of the immunobiology of the Guillain-Barré syndromes (GBS), the world's leading cause of acute autoimmune neuromuscular paralysis. Understanding the key pathophysiological pathways of GBS and developing rational, specific immunotherapies are essential steps towards improving the clinical outcome of this devastating disorder. Much of the research into GBS over the last decade has focused on the forms mediated by anti-ganglioside antibodies, and we have made substantial progress in our understanding in several related areas. Particular highlights include (a) the emerging correlations between anti-ganglioside antibodies and specific clinical phenotypes, notably between anti-GM1/anti-GD1a antibodies and the acute motor axonal variant and anti-GQ1b/anti-GT1a antibodies and the Miller Fisher syndrome; (b) the identification of molecular mimicry between GBS-associated Campylobacter jejuni oligosaccharides and GM1, GD1a, and GT1a gangliosides as a mechanism for anti-ganglioside antibody induction; (c) the development of rodent models of GBS with sensory ataxic or motor phenotypes induced by immunisation with GD1b or GM1 gangliosides, respectively. Our work has particularly studied the motor nerve terminal as a model site of injury, and through combined active and passive immunisation paradigms, we have developed murine neuropathy phenotypes mediated by anti-ganglioside antibodies. This has been achieved through use of glycosyltransferase and complement regulator knock-out mice, both for cloning anti-ganglioside antibodies and inducing disease. Through such studies, we have proven a neuropathogenic role for murine anti-ganglioside antibodies and human GBS-associated antisera and identified several determinants that influence disease expression including (a) the level of immunological tolerance to microbial glycans that mimic self-gangliosides; (b) the ganglioside density in target tissue; (c) the level of complement activation and the neuroprotective effects of endogenous complement regulators; and (d) the role of calcium influx through complement pores in mediating axonal injury. Such studies provide us with clear information on an antibody-mediated pathogenesis model for GBS and should lead to rational therapeutic testing of agents that are potentially suitable for use in humans.

Immunoadsorption of factor VIII inhibitors

PURPOSE OF REVIEW

Extracorporeal immunoadsorption is being increasingly applied in a variety of disorders. This approach is particularly suited to removal of antibodies or inhibitors to coagulation factor VIII and may be particularly useful before the administration of large amounts of expensive replacement or bypass therapy for patients with hemophilia who are bleeding, or patients undergoing immune tolerance therapy.

RECENT FINDINGS

In patients with inhibitors to factor VIII, several types of immunoadsorption therapy have been used, although reports are mainly anecdotal, consisting of relatively small numbers of persons. Nonetheless, the findings suggest that immunoadsorption may be clinically effective and cost-effective and should be considered early in the treatment of appropriate patients. New immunoadsorption technologies are being described for a variety of disorders, including hemophilia, and a new synthetic matrix of polystyrene beads functionalized with sulfonate and tyrosyl methylester groups for immunoadsorption removal of factor VIII inhibitors is intriguing.

SUMMARY

Although immunoadsorption was shown to be clinically effective in patients with inhibitors to factor VIII more than two decades ago, recent papers have emphasized the desirability of early implementation of the modality in the treatment plan. Immunoadsorption is relatively easy to perform with few adverse effects, but specialized equipment is required, and it should be performed in an experienced setting. Although potentially less costly than other (bypass) therapies, immunoadsorption is itself not inexpensive, and its comparative effectiveness with plasmapheresis and other management options for the dangerously bleeding patient with antibodies to factor VIII should be determined by multicenter randomized controlled trials. Interesting recent novel technical developments in the field may facilitate increased use of the procedure.