Synthetic sialylphosphatidylethanolamine derivatives bind to human influenza A viruses and inhibit viral infection

Heparan Sulfate and Sialic Acid in Viral Attachment: Two Sides of the Same Coin?

Sialic acids and heparan sulfates make up the outermost part of the cell membrane and the extracellular matrix. Both structures are characterized by being negatively charged, serving as receptors for various pathogens, and are highly expressed in the respiratory and digestive tracts. Numerous viruses use heparan sulfates as receptors to infect cells; in this group are HSV, HPV, and SARS-CoV-2. Other viruses require the cell to express sialic acids, as is the case in influenza A viruses and adenoviruses. This review aims to present, in a general way, the participation of glycoconjugates in viral entry, and therapeutic strategies focused on inhibiting the interaction between the virus and the glycoconjugates. Interestingly, there are few studies that suggest the participation of both glycoconjugates in the viruses addressed here. Considering the biological redundancy that exists between heparan sulfates and sialic acids, we propose that it is important to jointly evaluate and design strategies that contemplate inhibiting the interactions of both glycoconjugates. This approach will allow identifying new receptors and lead to a deeper understanding of interspecies transmission.

Design and Functional Analysis of Heterobifunctional Multivalent Phage Capsid Inhibitors Blocking the Entry of Influenza Virus

Multiple conjugation of virus-binding ligands to multivalent carriers is a prominent strategy to construct highly affine virus binders for the inhibition of viral entry into host cells. In a previous study, we introduced rationally designed sialic acid conjugates of bacteriophages (Qβ) that match the triangular binding site geometry on hemagglutinin spike proteins of influenza A virions, resulting in effective infection inhibition in vitro and in vivo. In this work, we demonstrate that even partially sialylated Qβ conjugates retain the inhibitory effect despite reduced activity. These observations not only support the importance of trivalent binding events in preserving high affinity, as supported by computational modeling, but also allow us to construct heterobifunctional modalities. Capsids carrying two different sialic acid ligand–linker structures showed higher viral inhibition than their monofunctional counterparts. Furthermore, capsids carrying a fluorescent dye in addition to sialic acid ligands were used to track their interaction with cells. These findings support exploring broader applications as multivalent inhibitors in the future.

Novel thiosialosides tethered to metal nanoparticles as potent influenza A virus haemagglutinin blockers

BACKGROUND

The purpose of this study was to develop a new class of influenza A virus haemagglutinin (HA) blockers by tethering thiosialoside molecules to metal nanoparticles and producing glycoclusters that enhance the affinity of HA binding by N-acetylneuraminic acid.

METHODS

Oxygen of the glycoside bond of sialoside was replaced with sulfur to prevent hydrolytic digestion of the N-acetylneuraminic acid residue by viral neuraminidase. Two novel thiosialosides, α-2-S-[p-(N-levulinyl)aminophenyl]-5-N-acetylneuraminic acid (Neu5Ac-S-Lev) and α-2-S-[m-(N-levulinyl)aminobenzyl]-5-N-acetylneuraminic acid (Neu5Ac-S-CH2-Lev), were tethered onto the surface of metal nanoparticles via an aminooxy functionalized thiol linker in a glycoblotting reaction. Gold (Au) and silver (Ag) nanoparticles were coated simultaneously with 11-mercaptoundecyl phosphorylcholine to reduce non-specific adsorption of proteins. Phosphorylcholine self-assembled monolayer-coated metals displaying clustered Neu5Ac (Neu5Ac-PCSAM-Au and Neu5Ac-PCSAM-Ag) were subjected to haemagglutination inhibition (HI) assays using the influenza A virus strain A/PR/8/1934 (H1N1).

RESULTS

Glyconanoparticles with thiosialosides had potent HI activities. In particular, Neu5Ac-PCSAM-Au with a diameter of 20 nm corresponding to 9.8 μM monosaccharide Neu5Ac was the most potent HA inhibitor. The versatility of this strategy was demonstrated by similar submicromolar HI activities of Neu5Ac-PCSAM-Ag with diameters of 50 nm and 150 nm.

CONCLUSIONS

Glycosylated metal nanoparticles were designed and synthesized as potent influenza A virus HA blockers. This study may contribute to the acceleration of the discovery of a new class of nanoparticle anti-influenza drugs.

Mechanisms of the action of povidone-iodine against human and avian influenza A viruses: its effects on hemagglutination and sialidase activities

Background

Influenza virus infection causes significant morbidity and mortality and has marked social and economic impacts throughout the world. The influenza surface glycoproteins, hemagglutinin (HA) and neuraminidase (NA), act cooperatively to support efficient influenza A virus replication and provide the most important targets for anti-influenza chemotherapy. In this study, povidone-iodine (PVP-I), which has a broad-spectrum microbicidal property, was examined for its inhibitory effects against influenza virus infection in MDCK cells and the mechanisms of PVP-I action on HA and NA were revealed.

Results

Results obtained using a novel fluorescence- and chromogenic-based plaque inhibition assay showed that 1.56 mg/ml PVP-I inhibited infections in MDCK cells of human (8 strains) and avian (5 strains) influenza A viruses, including H1N1, H3N2, H5N3 and H9N2, from 23.0–97.5%. A sialidase inhibition assay revealed that PVP-I inhibited N1, N2 and N3 neuraminidases with IC₅₀ values of 9.5–212.1 μg/ml by a mixed-type inhibition mechanism. Receptor binding inhibition and hemagglutinin inhibition assays indicated that PVP-I affected viral hemagglutinin rather than host-specific sialic acid receptors.

Conclusion

Mechanisms of reduction of viral growth in MDCK cells by PVP-I involve blockade of viral attachment to cellular receptors and inhibition of viral release and spread from infected cells. Therefore, PVP-I is useful to prevent infection and limit spread of human and avian influenza viruses.

Chemoenzymatic synthesis of artificial glycopolypeptides containing multivalent sialyloligosaccharides with a γ-polyglutamic acid backbone and their effect on inhibition of infection by influenza viruses

Highly water-soluble, artificial glycopolypeptides with a gamma-polyglutamic acid (gamma-PGA) backbone derived from Bacillus subtilis sp. and multivalent sialyloligosaccharide units have been chemoenzymatically synthesized as potential polymeric inhibitors of infection by bird and human influenza viruses. 5-Trifluoroacetamidopentyl beta-N-acetyllactosaminide and 5-trifluoroacetamidopentyl beta-lactoside were enzymatically synthesized from LacNAc and lactose, respectively, by cellulase-mediated condensation with 5-trifluoroacetamido-1-pentanol. After deacetylation, the resulting 5-aminopentyl beta-LacNAc and beta-lactoside glycosides were coupled to the alpha-carboxyl groups of the gamma-PGA side chains. The artificial glycopolypeptides carrying LacNAc and lactose were further converted to Neu5Acalpha2-(3/6)Galbeta1-4Glcbeta and Neu5Acalpha2-(3/6)Galbeta1-4GlcNAcbeta sialyloligosaccharide units by alpha2,3- and alpha2,6-sialyltransferase, respectively. The interaction of these glycopolypeptides with various influenza virus strains has been investigated by three different methods. Glycopolypeptides carrying Neu5Acalpha2,6LacNAc inhibited hemagglutination mediated by influenza A and B viruses, and their relative binding affinities for hemagglutinin were 10(2)- to 10(4)-fold higher than that of the naturally occurring fetuin control. A glycopolypeptide carrying Neu5Acalpha2,6LacNAc inhibited infection by A/Memphis/1/71 (H3N2) 93 times more strongly than fetuin, as assessed by cytopathic effects on virus-infected MDCK cells. The avian virus [A/duck/Hong kong/4/78 (H5N3)] bound strongly to Neu5Acalpha2,3LacNAc/Lac-carrying glycopolypeptides, whereas the human virus [A/Memphis/1/71 (H3N2)] bound to Neu5Acalpha2,6LacNAc in preference to Neu5Acalpha2,6Lac. Taken together, these results indicate that the binding of viruses to terminal sialic acids is markedly affected by the structure of the asialo portion, in this case either LacNAc or lactose, in the sugar chain of glycopolypeptides.

Edible bird's nest extract inhibits influenza virus infection

Edible bird's nest (EBN) is the nest of the swift that is made from its saliva. Although EBN has been widely used for enhancing immunocompetence, its antiviral efficacy has not been studied in detail. We found that EBN extract could strongly inhibit infection with influenza viruses in a host range-independent manner when it was hydrolyzed with Pancreatin F. Western blotting assay showed that the EBN extract bound to influenza virus. Furthermore, EBN extract could neutralize the infection of MDCK cells with influenza viruses and inhibit hemagglutination of influenza viruses to erythrocytes, but it could not inhibit the activity of influenza virus sialidase. Fluorometric HPLC indicated that the major molecular species of sialic acid in EBN is N-acetylneuraminic acid. The results suggest that EBN is a safe and valid natural source for the prevention of influenza viruses.

Sialobiology of influenza: molecular mechanism of host range variation of influenza viruses

The gene pool of influenza A viruses in aquatic birds provides all of the genetic diversity required for human and lower animals. Host range selection of the receptor binding specificity of the influenza virus hemagglutinin occurs during maintenance of the virus in different host cells that express different receptor sialo-sugar chains. In this paper, functional roles of the hemagglutinin and neuraminidase spikes of influenza viruses are described in the relation to 1) host range of influenza viruses, 2) receptor binding specificity of human and other animal influenza viruses, 3) recognition of sialyl sugar chains by Spanish influenza virus hemagglutinin, 4) highly pathogenic and potentially pandemic H5N1, H9N2, and H7N7 avian influenza viruses and molecular mechanism of host range variation of influenza viruses, 5) role of the neuraminidase spike for the host range of influenza viruses, and 6) Development of anti-influenza drugs.

Efficient synthesis of glyceroyl beta-lactoside and its derivatives through a condensation reaction by cellulase

Condensation reaction between lactose and glycerol was effectively catalyzed by utilizing a commercially available cellulase preparation from Trichoderma reesei. The enzyme induced the formation of 1-O-beta-lactosyl-(R,S)-glycerol (1) and 2-O-beta-lactosyl glycerol (2) in a molar ratio of 7:3 and in a 20% yield based on lactose added. The enzyme also induced the condensation of lactose with 1,3-propanediol to produce O-beta-lactosyl propanediol (3) in a yield of 15%. When various alkanols (N: 2-8) and allyl alcohol were used in the condensation reaction, the corresponding alkyl and allyl beta-lactoside were obtained in the yields of 0.9-3.8% of the desired compounds.

An O-glycoside of sialic acid derivative that inhibits both hemagglutinin and sialidase activities of influenza viruses

The compound Neu5Ac3alphaF-DSPE (4), in which the C-3 position was modified with an axial fluorine atom, inhibited the catalytic hydrolysis of influenza virus sialidase and the binding activity of hemagglutinin. The inhibitory activities to sialidases were independent of virus isolates examined. With the positive results obtained for inhibition of hemagglutination and hemolysis induced by A/Aichi/2/68 virus, the inhibitory effect of Neu5Ac3alphaF-DSPE (4) against MDCK cells was examined, and it was found that 4 inhibits the viral infection with IC50 value of 5.6 microM based on the cytopathic effects. The experimental results indicate that compound 4 not only inhibits the attachment of virus to the cell surface receptor but also disturbs the release of the progeny viruses from infected cells by inhibiting both hemagglutinin and sialidase of the influenza viruses. The study suggested that the compound is a new class of bifunctional drug candidates for the future chemotherapy of influenza.