Structure-based inhibitors of influenza virus sialidase. A benzoic acid lead with novel interaction

Influenza virus sialidase is a surface enzyme that is essential for infection of the virus. The catalytic site is highly conserved among all known influenza variants, suggesting that this protein is a suitable target for drug intervention. The most potent known inhibitors are analogs of 2-deoxy-2,3-didehydro-N-acetylneuraminic acid (Neu5Ac2en), particularly the 4-guanidino derivative (4-guanidino-Neu5Ac2en). We utilized the benzene ring of 4-(N-acetylamino)benzoic acids as a cyclic template to substitute for the dihydropyran ring of Neu5Ac2en. In this study several 3-(N-acylamino) derivatives were prepared as potential replacements for the glycerol side chain of Neu5Ac2en, and some were found to interact with the same binding subsite of sialidase. Of greater significance was the observation that the 3-guanidinobenzoic acid derivative (equivalent to the 4-guanidino grouping of 4-guanidino-Neu5Ac2en), the most potent benzoic acid inhibitor of influenza sialidase thus far identified (IC50 = 10 microM), occupied the glycerol-binding subsite on sialidase as opposed to the guanidino-binding subsite. This benzoic acid derivative thus provides a new compound that interacts in a novel manner with the catalytic site of influenza sialidase.

Sialic acid and oxidizability of low density lipoprotein subfractions of hyperlipidemic patients

OBJECTIVES

Low density lipoprotein (LDL) does not constitute an homogenous fraction and it is known that the heavy LDL subfraction is potentially more atherogenic than the light one. Because concentration of LDL subfractions tend to be different in hyperlipidemias, it was verified whether these subfractions can also differ in sialic acid and neutral sugar content, as well as their resistance to oxidation.

DESIGN AND METHODS

Two subfractions of low density lipoprotein (light LDL, density 1.019-1.034 g/mL and heavy LDL, density 1.034-1.063 g/mL) were isolated from the plasma of 17 patients with hypercholesterolemia, 11 with combined hyperlipidemia, 7 with hypertriglyceridemia, and 19 normolipidemic subjects. The content of sialic acids and neutral sugars of apo B was determined, respectively, by the periodate-thiobarbituric acid method and by reaction with phenol. The oxidation of LDL subfractions was determined by exposure to 5 microM copper (II) followed by the measurement of lipid hydroperoxides production by high performance liquid chromatography with electrochemical detection.

RESULTS

The study groups did not differ in the neutral sugar content of LDL subfractions. However, compared to normolipidemic subjects, the sialic acid concentration of both LDL subfractions was lower in patients with hypercholesterolemia and hypertriglyceridemia and higher in those with combined hyperlipidemia (p < 0.05). In the hypercholesterolemia and combined hyperlipidemia groups, the lipid hydroperoxide content (microM) of heavy LDL was higher than in normolipidemic subjects (p < 0.05).

CONCLUSIONS

The heavy LDL subfraction was more susceptible to oxidation in the patients with combined hyperlipidemia compared to controls and the other hyperlipidemic groups. The effect of sialic acids on heavy LDL oxidizability seems to vary according to the type of hyperlipidemia.

[The stimulating effect of sialic acid on the processes of postradiation hemopoietic regeneration]

The possibility of stimulating hemopoiesis inhibited by irradiation with N-acetylneuraminic acid (N-ANA) and the mechanisms of this stimulating effect are considered. A 3-fold N-ANA injection (total dose 150 mg/kg) on days 3, 4, and 5 after irradiation mainly promote the activation of erythropoiesis in the bone marrow. A reliable increase in the amount of erythrokaryocytes in the bone marrow and erythroid colony formation from erythroid precursors (CFU-E) were observed in mice CBA irradiated in a dose of 2.0 g and then received N-ANA. A rise in erythropoietic activity production by bone marrow cells testified that elevation of hemopoiesis inducing microenvironment function is the base of stimulating effect of N-ANA on hemopoiesis.

Abnormal synthesis of dolichol-linked oligosaccharides in carbohydrate-deficient glycoprotein syndrome

Carbohydrate-deficient glycoprotein syndrome (CDGS) is a rare metabolic disorder presenting in infancy with severe neurologic involvement and variable multisystemic abnormalities. Diagnosis relies upon the detection of abnormal serum glycoprotein isoforms on isoelectric focusing (IEF) gels. Carbohydrate structural analyses were performed on the N-linked oligosaccharides of serum alpha 1-antitrypsin (alpha-1AT) from two Danish children with classical type I CDGS. Following preparative gel electrophoresis of alpha-1AT isoforms, oligosaccharide charge and monosaccharide composition analyses revealed increased glycosylation heterogeneity in CDGS compared with normal alpha-1AT. CDGS alpha-1AT isoforms bore N-glycans co-migrating with monosialylated standards, while normal alpha-1AT oligosaccharides co-migrated with both mono- and disialylated standards. While the monosaccharide contents of normal alpha-1AT isoforms were relatively uniform, those of CDGS alpha-1AT isoforms varied widely, and many were relatively mannose enriched. The mannose-rich oligosaccharides of CDGS alpha-1AT were not typical oligomannose structures since they were not released by endo-beta-N-acetylglucosaminidase H (endo H) digestion. Metabolic labelling of CDGS fibroblasts with [3H]mannose showed lower than normal intracellular total mannose, free mannose and phosphorylated mannose species, as well as diminished [3H]mannose incorporation into dolichol-linked and protein-linked oligosaccharides. In addition, the glycans liberated from CDGS dolichol-linked oligosaccharides were significantly truncated compared with those from normal fibroblasts. These data suggest that our type I CDGS patients produce abnormal N-linked oligosaccharides due to impaired biosynthesis of dolichol-oligosaccharide precursors.

2,3-didehydro-2,4-dideoxy-4-guanidino-N-acetyl-D-neuraminic acid (4-guanidino-Neu5Ac2en) is a slow-binding inhibitor of sialidase from both influenza A virus and influenza B virus

The effect of 2,3-didehydro-2,4-dideoxy-4-guanidino-N-acetyl-D-neuraminic acid (4-guanidino-Neu5Ac2en) on the sialidases from influenza virus reassortant X31 (which contains the sialidase from A/Aichi/2/68) and influenza virus B/Beijing/1/87 has been investigated. We find that 4-guanidino-Neu5Ac2en is a slow-binding inhibitor of both influenza A and influenza B virus sialidase, and that association and dissociation rate constants are almost identical for both enzymes. Furthermore, values for these rate constants are independent of whether purified enzyme or detergent-treated virus is used in the assays.

Carbohydrates mediate the adherence of hamster sperm to oviductal epithelium

The lower isthmus of the mammalian oviduct appears to serve as a reservoir for sperm that are retained by adherence to the epithelium. By inhibiting sperm binding within excised hamster oviducts and making use of carbohydrate probes, we have characterized the adherence of sperm in the reservoir and established a potential biochemical mechanism for the adherence and release of sperm. Fetuin and its terminal sugar, N-acetylneuraminic acid, interfered with the adherence of sperm to the oviductal epithelium. Labeled fetuin bound to the acrosomal region of fresh epididymal sperm, but not hyperactivated sperm, which have previously been reported to release from epithelial binding. Western blots labeled with fetuin and sialic acid-recognizing lectins identified proteins at several molecular masses that are candidates for the sperm surface component involved in adherence. Labeling of some of these candidates was reduced in samples from hyperactivated sperm. These results indicate that a sialylated oligosaccharide similar to that found on fetuin may be recognized by a sperm surface component and mediate binding to the oviductal epithelium. Release may be accomplished by loss or modification of the component during capacitation or hyperactivation.

4-Guanidino-Neu5Ac2en fails to protect chickens from infection with highly pathogenic avian influenza virus

The effectiveness of the novel sialidase inhibitor 4-guanidino-Neu5Ac2en, which is highly effective in mouse and ferret models of influenza virus infection (von Itzstein et al. (1993) Nature 363, 418-423), has been assessed as a prophylactic agent in the prevention of infection of chickens with highly pathogenic avian influenza viruses. At best a small delay in the onset of pyrexia and death was observed with one strain of fowl plague virus, but not with two other strains. These results demonstrate that a locally acting drug may be ineffective if virus can escape from the site of inoculation and replicate elsewhere.

Characterization of CD33 as a new member of the sialoadhesin family of cellular interaction molecules

CD33 is a member of the Ig superfamily that is restricted to cells of the myelomonocytic lineage but whose functions and binding properties are unknown. It shares sequence similarity with sialoadhesin, CD22, and the myelin-associated glycoprotein, which constitute the Sialoadhesin family of sialic acid-dependent cell adhesion molecules. In the present study, we show that CD33 is a fourth member of this family. As a model for sialic acid-dependent binding, human erythrocytes were derivatized with N-acetylneuraminic acid (NeuAc) in different linkages. A recombinant soluble form of CD33, Fc-CD33, bound red blood cells with a specificity similar to that of sialoadhesin, preferring NeuAc alpha 2,3Gal in N- and O-glycans over NeuAc alpha 2,6Gal in N-glycans. Fc-CD33 also bound selectively to the myeloid cell lines HL-60 and U937. However, CD33 was unable to mediate cell binding after transient expression in COS cells, despite high levels of surface expression. Pretreatment of the CD33-transfected cells with sialidase rendered them capable of mediating sialic acid-dependent binding. These results show that CD33 can function as a sialic acid-dependent cell adhesion molecule and that binding can be modulated by endogenous sialoglycoconjugates when CD33 is expressed in a plasma membrane.

Identification of gangliosides as inhibitors of ADP-ribosyltransferases of pertussis toxin and exoenzyme C3 from Clostridium botulinum

We have previously reported the presence of an endogenous inhibitory activity in bovine brain for the ADP-ribosylation of GTP-binding proteins catalyzed by pertussis toxin (PT) (Hara-Yokoyama, M., and Furuyama, S. (1989) Biochem. Biophys. Res. Commun. 160, 67-71). In the present study, we identified the inhibitor as a ganglioside. The screening of various gangliosides revealed that GQ1b alpha most effectively inhibited the ADP-ribosyltransferase activities of both the holoenzyme and the catalytic subunit of PT. GQ1b alpha is a ganglioside newly identified as one of the antigens recognized by the cholinergic neuron-specific antibody, anti-Chol-1 alpha (Hirabayashi, Y., Nakao, T., Irie, F., Whittaker, V.P., Kon, K., and Ando, S. (1992) J. Biol. Chem. 267, 12973-12978). GQ1b alpha also inhibited the PT-catalyzed NAD+ glycohydrolysis. Unlike PT activity, the ADP-ribosylation and the NAD+ glycohydrolysis catalyzed by the C3 exoenzyme from Clostridium botulinum type C were inhibited by GT1b and GQ1b. The ADP-ribosylation catalyzed by either PT or the C3 exoenzyme was not inhibited by ceramide, galactocerebroside, or sialic acid. In addition to the inhibitory action of gangliosides on ADP-ribosylation, the importance of gangliosides as regulators of NAD+ metabolism is discussed.

Binding of human plasma sialoglycoproteins by the B cell-specific lectin CD22. Selective recognition of immunoglobulin M and haptoglobin

CD22 is a cell-surface receptor of resting mature B cells that recognizes sialic acid (Sia) in the natural structure Sia alpha 2-6Gal beta 1-4GlcNAc (Powell, L. D., Jain, R. K., Matta, K. L., Sabesan, S., and Varki, A. (1995) J. Biol. Chem. 270, 7523-7532). Human umbilical vein endothelial cells (HEC) treated with inflammatory cytokines such as tumor necrosis factor-alpha (TNF-alpha) display increases in cell-surface CD22 ligands, caused by increased expression of the enzyme beta-galactoside alpha 2,6-sialyltransferase (Hanasaki, K., Varki, A., Stamenkovic, I., and Bevilacqua, M. P. (1994) J. Biol. Chem. 269, 10637-10643; Hanasaki, K., Varki, A., and Powell, L. D. (1995) J. Biol Chem. 270, 7533-7542). Thus, CD22 could direct potential interactions between mature B cells and endothelial cells during inflammatory states. However, this would have to occur in the presence of blood plasma, which contains many sialoglycoproteins known to carry alpha 2-6-linked sialic acids. We show here that human plasma can indeed inhibit Sia-dependent binding of a recombinant soluble chimeric form of human CD22 (CD22Rg) to TNF-alpha activated HEC. Affinity adsorption of individual human plasma samples with immobilized CD22Rg showed that, of the numerous alpha 2-6-sialic acid containing glycoproteins in plasma, only three polypeptides with apparent molecular mass (under reducing conditions) of 74, 44, and 25 kDa bound, and were specifically eluted with alpha 2-6-sialyllactose. NH2-terminal amino acid sequencing of these high affinity CD22 ligands revealed that they are subunits of immunoglobulin M (IgM) and haptoglobin. Purified human IgM from pooled human plasma can be quantitatively bound by CD22Rg, and binding is blocked by alpha 2-6-sialyllactose, but not by alpha 2-3-sialyllactose. Pretreatment by sialidase or by mild periodate oxidation of sialic acid side chains abolishes these interactions. IgM at physiological concentrations also inhibits CD22Rg binding to TNF-alpha-activated HEC in a manner dependent not only upon its sialylation but also requiring its intact multimeric structure. These data show that CD22 is capable of highly selective recognition of certain multimeric plasma sialoglycoproteins that carry alpha 2-6-linked sialic acids. Notably, the two proteins that are selectively recognized are known to be involved in immune and inflammatory responses. Haptoglobin synthesis by the liver is markedly increased during the "acute phase response" to systemic inflammation, while IgM is the major product resulting from activation of resting CD22-positive B cells.

Structures of aromatic inhibitors of influenza virus neuraminidase

Neuraminidase (NA), a surface glycoprotein of influenza virus, is a potential target for design of antiinfluenza agents. The crystal structure of influenza virus neuraminidase showed that in the active site 11 residues are universally conserved among all strains known so far. Several potent inhibitors based on the carbohydrate compound 2-deoxy-2,3-didehydro-D-N-acetylneuraminic acid (DANA) have been shown to bind to the conserved active site and to reduce virus infection in animals when administered by nasal spray. Inhibitors of this type are, however, rapidly excreted from physiological systems and may not be effective in order to provide long-time protection. A new class of specific NA inhibitors, which are benzoic acid derivatives, has been designed on the basis of the three-dimensional structure of the NA-DANA complex and modeling of derivatives of 4-(acetylamino)benzoic acid in the NA active site. Intermediates were synthesized and were shown to moderately inhibit the NA activity and to bind to the NA active site as predicted. These rudimentary inhibitors, 4-(acetylamino)-3-hydroxy-5-nitrobenzoic acid, 4-(acetylamino)-3-hydroxy-5-aminobenzoic acid, and 4-(acetylamino)-3-aminobenzoic acid, and their X-ray structures in complexes with N2 (A/Tokyo/3/67) and B/Lee/40 neuraminidases have been analyzed. The coordinates of such inhibitors complexed with NA were used as the starting model for further design of more potent benzoic acid inhibitors. Because the active site residues of NA are invariant, the designed aromatic inhibitors have the potential to become an antiviral drug against all strains of influenza virus.

Activation of the Sendai virus fusion protein by receptor binding

2,3 Dehydro-2-deoxy-N-acetyl-neuraminic acid (DNANA) competitively inhibits the neuraminidase activity of Hemagglutinin-neuraminidase (HN) from Sendai virus. The inhibition constant depends on the presence of the Fusion (F) protein, which is 30 microM in the presence of active F protein and 50 microM when the F protein is inactivated. These data correlate with previously reported evidence of interaction of the F protein with HN (Dallocchio, F., Tomasi, M., & Bellini, T. (1994) Biochem. Biophys. Res. Comm. 201, 988-993). Desialyzation of erythrocytes, by Clostridium neuraminidase, lowers the hemolytic activity of SV to < 0.1% of that observed on untreated erythrocytes. However, addition of DNANA causes a concentration-dependent increase of hemolytic activity. Both HN and the F protein are required for the activation of hemolytic activity by DNANA. The affinity constant for DNANA, calculated from the activation of hemolytic activity on desialyzed erythrocytes, is 35 microM, very close to the Ki for neuraminidase activity. These data suggest that the binding of the F protein to HN, induced by the binding to HN of a substrate or a substrate analogue, causes a conformational change which activates the F protein.

Inhibition of cholera toxin by human milk fractions and sialyllactose

The effects of human milk fractions on clolera toxin B subunit binding to monosialoganglioside 1 (GM1) were investigated. Human milk, human defatted milk, whey, and a low-molecular-weight fraction of human milk inhibited the binding, but casein did not inhibit it. The inhibitory activity of whey from bovine-milk-based infant formula was less than that of whey from human milk. Differences in composition between human and bovine whey seemed to influence the extent of the inhibitory activity. Sialylated oligosaccharides were considered to be the possible components that inhibited cholera toxin. The effects of sialyllactose, a predominant sialylated component of human milk, on cholera toxin-induced diarrhea were investigated by the rabbit intestinal loop method. Sialyllactose inhibited the cholera toxin inducing fluid accumulation, although neither sialic acid nor lactose had an effect on it. The results suggest that sialyllactose is responsible for the inhibitory activity of milk on cholera toxin.

The specificity of the binding site of AchatininH, a sialic acid-binding lectin from Achatina fulica

A sialic acid-binding lectin, AchatininH (ATNH), having unique specificity towards 9-O-acetylneuraminic acid, has been purified and characterized. The specificity of this lectin for O-acetylsialic acids was studied in detail, using various sialic acid derivatives and sialoglycoproteins. The potent inhibition of hemagglutination by bovine submaxillary mucin (BSM), which contains 9(7,8)-O-acetylsialic acid and by free 9-O-acetylneuraminic acid confirms the preferential affinity towards this sugar. Further support for the role of O-acetylsialic acid was obtained by sialidase treatment of BSM. O-Deacetylation of the sialic acid residue abolished its inhibitory potency. Moreover, when the trihydroxypropyl side chain of the sialic acid molecule was modified by periodate-borohydride treatment, the truncated C7-sialic acid was unable to bind ATNH. This result suggests that the glycerol side chain of Neu5Ac, especially the C-8 and/or C-9 portion is an important determinant for ATNH. The hemagglutination-inhibition results using several mono-, di-, and tri-saccharides containing terminal sialic acid and various sialoglycoproteins reveals that ATNH preferentially binds the alpha-(2-->6)-linked sialic acid. Furthermore, beta-D-GlcNAc-(1-->3)-[alpha-NeuGc-(2-->6)]-GalNAc-ol was found to be the best ligand for ATNH.

A sialic acid-derived phosphonate analog inhibits different strains of influenza virus neuraminidase with different efficiencies

A phosphonate analog of N-acetyl neuraminic acid (PANA) has been designed as a potential neuraminidase (NA) inhibitor and synthesized as both the alpha (ePANA) and beta (aPANA) anomers. Inhibition of type A (N2) and type B NA activity by ePANA was approximately a 100-fold better than by sialic acid, but inhibition of type A (N9) NA was only ten-fold better than by sialic acid. The aPANA compound was not a strong inhibitor for any of the NA strains tested. The crystal structures at 2.4 A resolution of ePANA complexed to type A (N2) NA, type A (N9) NA and type B NA and aPANA complexed to type A (N2) NA showed that neither of the PANA compounds distorted the NA active site upon binding. No significant differences in the NA-ePANA complex structures were found to explain the anomalous inhibition of N9 neuraminidase by ePANA. We put forward the hypothesis that an increase in the ePANA inhibition compared to that caused by sialic acid is due to (1) a stronger electrostatic interaction between the inhibitor phosphonyl group and the active site arginine pocket and (2) a lower distortion energy requirement for binding of ePANA.

Biochemical characterization of sheep platelet acetylcholinesterase after detergent solubilization

The biochemical characterization of detergent-solubilized acetylcholinesterase (AChE) from subcellular particles of sheep platelets and the effects of different effectors on AChE activity from solubilized platelet crude membranes have been undertaken and studied. Solubilization of AChE with detergent increased the thermal stability of the enzyme from all particulate fractions. Solubilized AChE from the mitochondria-granule fraction was the most thermostable at 55 degrees C. The Km values against acetylthiocholine chloride and the Arrhenius plot obtained were very similar for the AChE from all the solubilized fractions. There were no differences in the ability of solubilized AChE from different subcellular fractions to bind concanavalin A (Con A). In solubilized platelet crude membranes, benzyl alcohol was a potent AChE inhibitor at a concentration of 10(-2) M, whereas ethanol was not. Mg2+ cations and, to a lesser extent, Ca2+ and Mn2+ cations, activated AChE at concentrations higher than 1 mM. Serine hydrolase inhibitors and cholinesterase-specific inhibitors were very effective in the inactivation of AChE, whereas EDTA and EGTA had no effect. Of all the monosaccharides tested, only N-acetylneuraminic acid exerted an inhibitory effect on AChE activity. Immobilized-lectin binding studies demonstrated the interaction of solubilized crude membrane-bound AChE with Con A, lentil lectin and wheat germ agglutinin. Taken together, these data suggest the presence of a unique form of the membrane-bound AChE which has at least alpha-mannose and N-acetylglucosamine residues in the glycan chain.

Chemoreceptor-mediated polymerization and depolymerization of actin in hair bundles of sea anemones

Hair bundles located on tentacles of sea anemones are morphodynamic mechanoreceptors employed to regulate discharge of nematocysts into swimming prey. Activation of chemoreceptors for N-acetylated sugars is known to induce anemone hair bundles to elongate while shifting discharge to lower frequencies matching those produced by calmly swimming prey. In the continued presence of N-acetylated sugars, activation of proline receptors is known to induce hair bundles to shorten while shifting nematocyst discharge to higher frequencies presumed to correspond to movements produced by wounded, struggling prey. In the present study, N-acetylneuraminic acid (NANA) causes stereocilia to become more intensely fluorescent in confocal optical sections of phalloidin-stained specimens, suggesting that receptors for N-acetylated sugars initiate processes to increase the density of F-actin within stereocilia. Computer analysis of electron micrographs is consistent with this interpretation for large diameter stereocilia but not for small diameter stereocilia. In the continued presence of NANA, proline causes fluorescence intensity of phalloidin to decrease to or below control levels. DNaseI uniformly stains large diameter stereocilia, suggesting that these stereocilia contain a pool of G-actin. Fluorescence intensity of DNaseI in stereocilia is significantly less bright in specimens exposed to NANA alone than in specimens exposed to proline in the continued presence of NANA. It appears that whereas activated receptors for NANA induce G-actin to polymerize in large diameter stereocilia, activated receptors for proline induce F-actin to depolymerize, restoring G-actin pools.

Regulation of B cell:T cell interactions: potential involvement of an endogenous B cell sialidase

In light of the ability of B cells treated with neuraminidase to interact more effectively with T cells, the increased capacity of activated, but not small resting B cells, to interact with T cells could be associated with the level of sialylation on certain B cell surface molecules which influences the effectiveness of the physical interaction between B and T cells. The purpose of this study was to determine if activation of B cells altered sialylation via an endogenous sialidase which affected both the initial interaction between T and B cells and subsequent B cell-induced T cell proliferation. The competitive neuraminidase inhibitor, 2-deoxy-2,3-dehydro-N-acetylneuraminic acid (NeuAc2en), inhibited LPS-mediated enhancement of B cell conjugate formation with Ia-specific T cell clones as well as enhancement of their capacity to stimulate a mixed lymphocyte reaction. The addition of NeuAc2en during LPS stimulation did not affect the surface expression of Ia, LFA-1, ICAM-1 or mB7, suggesting that inhibition of LPS-mediated enhancement by the sialidase inhibitor was not due to changes in the level of expression of the major B cell adhesion or co-stimulatory molecules. Short term stimulation with phorbol myristate acetate (PMA) and ionomycin also enhanced the ability of resting B cells to form antigen specific T:B conjugates. However, activation of B cells with PMA and ionomycin or with LPS did not change the capacity of a sialic acid specific lectin to bind to the B cells, suggesting that activation was not associated with global changes in surface sialic acid content. B cell stimulation did not appear to increase the activity of the most prevalent B cell sialidase activity as measured in an in vitro assay system, suggesting that the major B cell sialidase may not be responsible for the alteration of B cell sialylation levels or the ability of activated B cells to interact more effectively with T cells. The possibility of intracellular compartmentalization of sialidase activity or that a minor B cell sialidase may play a role in the regulation of a B cells ability to interact with T cells are discussed.

[Mono- and polyvalent synthetic sialosides as inhibitors of Mycoplasma pneumoniae adhesiveness]

Nine mono- and polyvalent sialosides as substances inhibiting adhesive properties of mycoplasma Mycoplasma pneumoniae--the agent of human atypical pneumonia have been studied in the reaction of hemagglutination (RHA) using solid-phase variant of ELISA-test ("sandwich"--variant), which is based on the competition for specific binding in RHA between the studied syalosides and sialylglycoproteins of fetuin conjugate with horseradish peroxidase. Of seven polymers--P alpha.12.ONa(N1), P alpha.12.EA(N2), P alpha.12.NH2(N3), P alpha.12.AES.10.ONa(N4), P alpha.12.Hg.20.ONa(N6), P20.SLea.NH2(N7), as well as monomer alpha-Bn Neu5Ac and fucoidan the polymers 5, 2, 4 and 7 in concentrations as to the content of sialic acid 1.0; 1.3; 1.35 and 10.0 M, respectively, most efficiently (up to 98%) inhibited the adhesiveness of M. pneumoniae. Polymeric sialosides 3, 6 and 1 proved less active and, the concentration of sialic acid in the composition of their molecules being 10.0 microM, inhibited adhesiveness of M. pneumoniae by approximately 77, 75 and 62.5%, respectively. Antiadhesive activity of fucoidan and monomer proved too low under concentration of these substances as to the content of sialic acid in them 25 microM: they decreased the ability to adhesion in M. pneumoniae by 33 and 56%, respectively. This proved that polyvalent sialosides 2, 4, 5 and 7 are promising for creation of drugs for treatment and prophylaxis of human pneumonias of mycoplasmal etiology on principally new basis with regard for the properties of the disease agent.

Inhibition of LPS-mediated cell activation in vitro and in vivo by gangliosides

Addition of purified GM1 gangliosides inhibited lipopolysaccharide (LPS)-stimulated proliferation of purified B cells by greater than 90%. Addition of gangliosides to B cells as late as 120 min after the addition of LPS still inhibited B-cell proliferation, suggesting that inhibition did not simply reflect direct binding of LPS to gangliosides. Gangliosides also inhibited proliferation of B cells stimulated by anti-Ig antibodies, albeit to a lesser degree than inhibition of the LPS-stimulated response. The finding that B-cell proliferation stimulated by the combination of PMA+ionomycin was also inhibited by gangliosides suggests that its inhibitory activity did not reflect interference with binding of the B-cell stimuli to membrane receptors. The inhibitory effect of gangliosides was not restricted to B cells, since LPS-induced TNF production by macrophages was also inhibited in vitro. The inhibitory activity of gangliosides was also seen in vivo, and mice injected with soluble gangliosides or implanted with slow-release pellets impregnated with gangliosides showed reduced TNF production in vivo in response to LPS. Mice that were implanted with these slow-release pellets were also protected from LPS-induced lethality. Thus, while only 10% of control mice survived injection with LPS+galactosamine, the experimental group showed a 64% survival. It is likely that this protective effect reflects the ability of gangliosides to suppress LPS-mediated TNF production. This model provides a basis for studying a regulatory role for gangliosides in B-cell activation in vitro and macrophage activation in vitro and in vivo. Furthermore, it suggests new approaches to suppress the toxic effects induced by LPS in vivo.

Anti-influenza virus activity of the neuraminidase inhibitor 4-guanidino-Neu5Ac2en in cell culture and in human respiratory epithelium

The anti-influenza activity of the neuraminidase inhibitor 4-guanidino-Neu5Ac2en (4-G-NAc) was determined in Madin-Darby canine kidney (MDCK) cells by yield reduction and ELISA and in explants of human respiratory epithelium by yield reduction. In MDCK cells, 50% inhibitory concentrations (EC50) averaged 0.5 microgram/ml for influenza A/Virginia/88(H3N2) and 0.04 microgram/ml for A/Texas/36/91(H1N1) by ELISA, and < 0.01 microgram/ml for influenza A/Virginia by yield reduction. In human adenoid explants, concentrations causing at least 1.0 log10 TCID50/ml decrease in yield (EC90) at 48 h were < 0.01 microgram/ml for A(H1N1) and A(H3N2) viruses and 0.25 microgram/ml for B/Hong Kong/5/72. 100 micrograms/ml 4-G-NAc did not inhibit outgrowth of human adenoid epithelium at 6 days, whereas ribavirin 10 micrograms/ml reduced outgrowth by > 50%. 4-G-NAc is a potent and selective inhibitor of clinical isolates of influenza A and B viruses in human respiratory epithelium.

Effects of sialic acids and the beta-drug adrenergic blocker, propranolol, on the dynamics of human alpha 1-acid glycoprotein: a fluorescence study

The effect of propranolol on the dynamics of human alpha 1-acid glycoprotein (orosomucoid) (sialylated and asialylated) was studied. 2-p-Toluidinylnaphthalene-6-sulfonate (TNS) bound to the protein was used as a probe. The results were identical for all samples. Excitation at the red edge of the absorption spectrum of TNS leads to an important shift (15 nm) of the fluorescence emission maximum of the probe. This reveals that emission of TNS occurs before relaxation of the amino acid dipole has time to occur. Emission from a non-relaxed state means that TNS molecules are bound tightly to the protein, a result confirmed by polarization studies. Sialic acid residues and propranolol do not affect the rigidity of the binding site of TNS.