Tatyana V. Pochechueva

Bio: Tatyana V. Pochechueva is an academic researcher from Russian Academy of Sciences. The author has contributed to research in topics: In vivo & Fucoidan. The author has an hindex of 8, co-authored 8 publications receiving 120 citations.

High molecular weight neoglycoconjugates for solid phase assays.

Abstract: Adsorption of a carbohydrate on solid phase is the necessary stage of the immunosorbent assay (ELISA) and analogous methods of the study of carbohydrate-protein interaction. Usually physical adsorption on polystyrene requires a high concentration of conjugated carbohydrate and, thus, enormous consumption of it. In this study, we explored two approaches allowing more rational use of oligosaccharide (Glyc). The first of them is based on the covalent immobilization of neoglycoconjugates on the NH(2)-modified polystyrene; the second one is based on the elevated adherence of high m.w. neoglycoconjugates to polystyrene. Covalent immobilization of polyacrylamide conjugates, Glyc-PAA, provided a possibility to solve the problem, but the nonspecific binding of antibodies in ELISA proved to be unacceptably high. At the same time, the increase of the Glyc-PAA m.w. from 30 kDa to 2,000 kDa allowed a 10-20 fold decrease of its consumption, when using physical adsorption, whereas the assay background remained at the low level. The amount of 2,000 kDa Glyc-PAA that is sufficient for the coating of a standard 96-well plate corresponds to the nanomole level of oligosaccharide, this providing a possibility to use saccharides that are available in a very limited amount when studying the carbohydrate-protein interaction with solid-phase techniques.

Design of the blood group AB glycotope.

Abstract: Although the nature of the blood groups A and B has been comprehensively studied for a long time, it is still unclear as to what exactly is the epitope that is recognized by antibodies having AB specificity, i.e. monoclonal and polyclonal antibodies which are capable of interacting equally well with the antigens GalNAcalpha 1-3(Fucalpha 1-2)Gal (A trisaccharide) and Galalpha 1-3(Fucalpha 1-2)Gal (B trisaccharide), but do not react with their common fragment Fucalpha 1-2Gal. We have supposed that besides Fucalpha 1-2Gal, A and B antigens have one more shared epitope. The trisaccharides A and B are practically identical from the conformational point of view, the only difference being situated at position 2 of Galalpha residue, i.e. trisaccharide A has a NHAc group, whereas trisaccharide B has a hydroxyl group (see formulas). We have hypothesized that the AB-epitope should be situated in the part of the molecule that is opposite to the NHAc group of GalNAc residue. In order to test this hypothesis we have synthesized a polymeric conjugate in such a way that de-N-acetylated A-trisaccharide is attached to a polymer via the nitrogen in position C-2 of the galactosamine residue. In this conjugate the supposed AB-epitope should be maximally accessible for antibodies from the solution, whereas the discrimination site of antigens A and B by the antibodies should be maximally hidden due to the close proximity of the polymer. Interaction with several anti-AB monoclonal antibodies revealed that a part of them really interacted with the synthetic AB-glycotope, thus confirming our hypothesis. Moreover, similar antibodies were revealed in the blood of healthy blood group 0 donors. Analysis of spatial models was performed in addition to identify the hydroxyl groups of Fuc, Galalpha, and Galbeta residues, which are particularly involved in the composition of the AB-glycotope.

Monomeric and multimeric blockers of selectins: comparison of in vitro and in vivo activity.

Abstract: The potency of the oligosaccharides SiaLex, SiaLea, HSO3Lex, and HSO3Lea, their conjugates with polyacrylamide (PAA, 40 kD), and other monomeric and polymeric selectin inhibitors has been compared with that of the polysaccharide fucoidan. The following assay systems were used: 1) a 96-well assay based either on the use of recombinant E-, P-, and L- selectins or an analogous assay with natural P-selectin isolated from human platelets; 2) a platelet-based P-selectin cell assay; and 3) a rat model of peritoneal inflammation. IC50 values for the neoglycoconjugate SiaLea-PAA were 6, 40, and 85 µM for recombinant E-, P-, and L-selectins, respectively; all monomeric inhibitors were about two orders of magnitude weaker. PAA-conjugates, containing as a ligand tyrosine-O-sulfate (sTyr) in addition to one of the sialylated oligosaccharides, were the most potent synthetic blockers in vitro. Compared with fucoidan, the most potent known P- and L-selectin blocker, the bi-ligand glycoconjugate HSO3Lea-PAA-sTyr displayed similar inhibitory activity in vitro towards L-selectin and about ten times lower activity towards P-selectin. All of the tested synthetic polymers displayed a similar ability to inhibit neutrophil extravasation in the peritonitis model (in vivo) at 10 mg/kg. The data provide evidence that monomeric SiaLex is considerably more effective as a selectin blocker in vivo than in vitro, whereas the opposite is true for fucoidan and the bi-ligand neoglycoconjugate HSO3Lea-PAA-sTyr.

Solid-phase assays for study of carbohydrate specificity of galectins

Abstract: We have recently shown that the carbohydrate-binding pattern of galectins in cells differs from that determined in artificial (non-cellular) test-systems. To understand the observed discrepancy, we compared several test-systems differing in the mode of galectin presentation on solid phase. The most representative system was an assay where the binding of galectin (human galectins-1 and -3 were studied) to asialofetuin immobilized on solid phase was inhibited by polyacrylamide glycoconjugates, Glyc-PAA. This approach permits us to range quantitatively glycans (Glyc) by their affinity to galectin, i.e. to study both high and low affinity ligands. Our attempts to imitate the cell system by solid-phase assay were not successful. In the cell system galectin binds glycoconjugates by one carbohydrate-recognizing domain (CRD), and after that the binding to the remaining non-bound CRD is studied by means of fluorescein-labeled Glyc-PAA. In an “imitation” variant when galectins are loaded on adsorbed asialofetuin or Glyc-PAA followed by revealing of binding by the second Glyc-PAA, the interaction was not observed or glycans were ordered poorly, unlike in the inhibitory assay. When galectins were adsorbed on corresponding antibodies (when all CRDs were free for recognition by carbohydrate), a good concentration dependence was observed and patterns of specificities were similar (though not identical) for the two methods; notably, this system does not reflect the situation in the cell. Besides the above-mentioned, other variants of solid-phase analysis of galectin specificity were tested. The results elucidate the mechanism and consequence of galectin CRD cis-masking on cell surface.

The ABO blood group system revisited: a review and update.

Abstract: The antigens of the ABO system were the first to be recognized as blood groups and actually the first human genetic markers known. Their presence and the realization of naturally occurring antibodies to those antigens lacking from the cells made sense of the erratic failure of blood transfusion hitherto and opened up the possibility of a safe treatment practice in life-threatening blood loss. Although initially apparently simple, the ABO system has come to grow in complexity over the years. The mass of knowledge relating to carbohydrate chemistry, enzymology, molecular genetics, and structural and evolutionary biology is now enormous thanks to more than a century of research using ABO as a principal model. This has provided us with data to form a solid platform of evidence-based transfusion and transplantation medicine used every day in laboratories and clinics around the globe. This review aims to summarize key findings and recent progress made toward further understanding of this surprisingly polymorphic system.

Polymer-Based Therapeutics

Abstract: 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 releva...

Targeted ultrasound contrast agent for molecular imaging of inflammation in high-shear flow.

Abstract: Targeted ultrasound contrast materials (gas-filled microbubbles carrying ligands to endothelial selectins or integrins) have been investigated as potential molecular imaging agents. Such microbubbles normally exhibit good targeting capability at the slower flow conditions. However, in the conditions of vigorous flow, binding may be limited. Here, we describe a microbubble capable of efficient binding to targets both in slow and fast flow (exceeding 4 dyne/cm 2 wall shear stress) using a clustered polymeric form of the fast-binding selectin ligand sialyl Lewis X. Microbubbles were prepared from decafluorobutane gas and stabilized with a monolayer of phosphatidylcholine, PEG stearate and biotin-PEG-lipid. Biotinylated PSLe x (sialyl Lewis X polyacrylamide) or biotinylated anti-P-selectin antibody (RB40.34) was attached to microbubbles via a streptavidin bridge. In a parallel plate flow chamber targeted adhesion model, PSLe x bubbles demonstrated specific adhesion, retention and slow rolling on P-selectin-coated plates. Efficiency of firm targeted adhesion to a P-selectin surface (140 molecules/mm 2 ) was comparable for antibody-carrying bubbles and PSLe x -targeted bubbles at 0.68 dyne/cm 2 shear stress. At fast flow (4.45 dyne/cm 2 ), PSLe x -targeted bubbles maintained their ability to bind, while antibody-mediated targeting dropped more than 20-fold. At lower surface density of P-selectin (7 molecules/mm 2 ), targeting via PSLe x was more efficient than via antibody under all the flow conditions tested. Negative control casein-coated plates did not retain bubbles in the range of flow conditions studied. To confirm echogenicity, targeted PSLe x -bubbles were visualized on P-selectin-coated polystyrene plates by ultrasound imaging with a clinical scanner operated in pulse inversion mode; control plates lacking targeted bubbles did not show significant acoustic backscatter. In vivo, in a murine model of inflammation in the femoral vein setting, targeting efficacy of intravenously administered PSLe x -microbubbles was comparable with targeting mediated by anti-P-selectin antibody, and significantly exceeded the accumulation of non-targeted control bubbles. In the inflamed femoral artery setting, PSLe x -mediated microbubble targeting was superior to antibody- mediated targeting. Copyright # 2006 John Wiley & Sons, Ltd.