Structure elucidation and antiviral activity of a cold water-extracted mannogalactofucan Ts1-1A from Trametes sanguinea against human cytomegalovirus in vitro

In this study, we purified a partially acetylated heteropolysaccharide (Ts1-1A) from the fruit bodies of Trametes sanguinea Lloyd through cold water extraction and serial chromatographic separation. The purified polysaccharide Ts1-1A (12.8 kDa) was characterized as a branched mannogalactofucan with a backbone of alternately connected 1,3-linked α-Fucp and 1,6-linked α-Galp, which was partially substituted by non-reducing end units of β-Manp at O-2 and O-3 positions of 1,6-linked α-Galp. Ts1-1A showed pronounced anti-human cytomegalovirus activity at the concentration of 200 and 500 μg/mL in systematical assessments including morphological changes, western blotting, qPCR, indirect immunofluorescence and tissue culture infective dose assays. Moreover, Ts1-1A exerted its antiviral activity at two distinct stages of viral proliferation manifesting as significantly inhibiting viral protein (IE1/2 and p52) expression and reducing viral gene (UL123, UL44 and UL32) replication in the HCMV-infected WI-38 cells. At viral attachment stage, Ts1-1A interacted with HCMV and prevented HCMV from attaching to its host cells. While at early phase of viral replication stage, Ts1-1A suppressed HCMV replication by downregulating NQO1 and HO-1 proteins related to oxidative stress as an antioxidant. To sum up, Ts1-1A is a promising anti-HCMV agent which could be developed for HCMV infection prevention and therapy.

Identification and evaluation of a novel tribenzamide derivative as an inhibitor targeting the entry of the respiratory syncytial virus

Human respiratory syncytial virus (RSV) is the leading cause of severe lower respiratory tract infections in infants, the elderly, and the immunocompromised, yet no licensed vaccine and only limited therapeutic options for prevention and treatment are available, which poses a global health challenge and emphasizes the urgent medical need for novel antiviral agents. In the current study, a novel potent small molecule inhibitor of RSV was identified by performing a screening and structure optimization campaign, wherein a naturally occurring dicaffeoylquinic acid (DCQA) compound served as a chemical starting point. The reported benzamide derivative inhibitor, designated as 2f, was selected for its improved stability and potent antiviral activity from a series of investigated structurally related compounds. 2f was well tolerated by cells and able to inhibit RSV infection with a half maximal inhibitory concentration (IC₅₀) of 35 nM and a favorable selectivity index (SI) of 3742. Although the exact molecular target for 2f is not known, in vitro mechanism of action investigations revealed that the compound inhibits the early stage of infection by interacting with RSV virion and interferes primarily with the attachment and potentially with the virus-cell fusion step. Moreover, intranasal administration of 2f to mice simultaneously or prior to intranasal infection with RSV significantly decreased viral load in the lungs, pointing to the in vivo potential of the compound. Our results suggest that 2f is a viable candidate for further preclinical development and evaluation as an antiviral agent against RSV infections.

Partial carbonization of quercetin boosts the antiviral activity against H1N1 influenza A virus

Inflenza A viruses (IAVs) are highly transmissible and pathogenic Orthomyxoviruses, which have led to worldwide outbreaks and seasonal pandemics of acute respiratory diseases, causing serious threats to public health. Currently used anti-influenza drugs may cause neurological side effects, and they are increasingly less effective against mutant strains. To help prevent the spread of IAVs, in this work, we have developed quercetin-derived carbonized nanogels (CNGs_Qur) that display potent viral inhibitory, antioxidative, and anti-inflammatory activities. The antiviral CNGs_Qur were synthesized by mild carbonization of quercetin (Qur), which successfully preserved their antioxidative and anti-inflammatory properties while also contributed enhanced properties, such as water solubility, viral binding, and biocompatibility. Antiviral assays of co-treatment, pre-treatment, and post-treatment indicate that CNGs_Qur interacts with the virion, revealing that the major antiviral mechanism resulting in the inhibition of the virus is by their attachment on the cell surface. Among them, the selectivity index (SI) of CNGs_Qur270 (>857.1) clearly indicated its great potential for clinical application in IAVs inhibition, which was much higher than that of pristine quercetin (63.7) and other clinical drugs (4-81). Compared with quercetin at the same dose, the combined effects of viral inhibition, antioxidative and anti-inflammatory activities impart the superior therapeutic effects of CNGs_Qur270 aerosol inhalation in the treatment of IAVs infection, as evidenced by a mouse model. These CNGs_Qur effectively prevent the spread of IAVs and suppress virus-induced inflammation while also exhibiting good in vivo biocompatibility. CNGs_Qur shows much promise as a clinical therapeutic agent against infection by IVAs.

The key amino acids of E protein involved in early flavivirus infection: viral entry

Flaviviruses are enveloped viruses that infect multiple hosts. Envelope proteins are the outermost proteins in the structure of flaviviruses and mediate viral infection. Studies indicate that flaviviruses mainly use envelope proteins to bind to cell attachment receptors and endocytic receptors for the entry step. Here, we present current findings regarding key envelope protein amino acids that participate in the flavivirus early infection process. Among these sites, most are located in special positions of the protein structure, such as the α-helix in the stem region and the hinge region between domains I and II, motifs that potentially affect the interaction between different domains. Some of these sites are located in positions involved in conformational changes in envelope proteins. In summary, we summarize and discuss the key envelope protein residues that affect the entry process of flaviviruses, including the process of their discovery and the mechanisms that affect early infection.

Swine interferon-induced transmembrane protein, sIFITM3, inhibits foot-and-mouth disease virus infection in vitro and in vivo

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Swine IFITM3 (sIFITM3) shares the conserved functional domains and amino acid residues with its human ortholog.

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sIFITM3 restricts FMDV infection in BHK cells.

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sIFITM3 disrupts FMDV viral attachment to the host cell surface.

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sIFITM3 protects suckling mice from FMDV challenge.

The interferon-induced transmembrane protein 3 (IFITM3) is a widely expressed potent antiviral effector of the host innate immune system. It restricts a diverse group of pathogenic, enveloped viruses, by interfering with endosomal fusion. In this report, the swine IFITM3 (sIFITM3) gene was cloned. It shares the functionally conserved CD225 domain and multiple critical amino acid residues (Y19, F74, F77, R86 and Y98) with its human ortholog, which are essential for antiviral activity. Ectopic expression of sIFITM3 significantly inhibited non-enveloped foot-and-mouth disease virus (FMDV) infection in BHK-21 cells. Furthermore, sIFITM3 blocked FMDV infection at early steps in the virus life cycle by disrupting viral attachment to the host cell surface. Importantly, inoculation of 2-day-old suckling mice with a plasmid expressing sIFITM3 conferred protection against lethal challenge with FMDV. These results suggest that sIFITM3 is a promising antiviral agent and that can safeguard the host from infection with FMDV.

Initial evidence on differences among Enterovirus 71, Coxsackievirus A16 and Coxsackievirus B4 in binding to cell surface heparan sulphate

Cell surface heparan sulphate (HS) mediates infection for many viruses from diverse families. We demonstrated significant antiviral potencies for a number of HS mimetics against a cloned strain of Enterovirus 71 (EV71) in a previous study. Thus, the involvement of HS in mediating viral infection of isolates of human enteroviruses was investigated in Vero and human neural cells in the present work. In both cell lines, heparin and pentosan polysulphate significantly inhibited both infection and attachment of low passage clinical isolates of EV71 and Coxsackievirus A16 (CVA16) but showed no affect on Coxsackievirus B4 (CVB4) (p < 0.05). In addition, enzymatic removal of cell surface HS by heparinase I prevented binding of the clinical EV71 by nearly 50 % but failed to significantly inhibit CVA16 or CVB4 binding in Vero cells. Overall, the findings of this study provides evidence that whilst highly sulphated domains of HS serve as an essential attachment co-receptor for EV71, HS might be used as an alternative attachment receptor by the other member of Human Enterovirus group A, CVA16. In addition, HS may not mediate early infection in CVB4.

Viral and cellular determinants involved in hepadnaviral entry

Hepadnaviridae is a family of hepatotropic DNA viruses that is divided into the genera orthohepadnavirus of mammals and avihepadnavirus of birds. All members of this family can cause acute and chronic hepatic infection, which in the case of human hepatitis B virus (HBV) constitutes a major global health problem. Although our knowledge about the molecular biology of these highly liver-specific viruses has profoundly increased in the last two decades, the mechanisms of attachment and productive entrance into the differentiated host hepatocytes are still enigmatic. The difficulties in studying hepadnaviral entry were primarily caused by the lack of easily accessible in vitro infection systems. Thus, for more than twenty years, differentiated primary hepatocytes from the respective species were the only in vitro models for both orthohepadnaviruses (e.g. HBV) and avihepadnaviruses (e.g. duck hepatitis B virus [DHBV]). Two important discoveries have been made recently regarding HBV: (1) primary hepatocytes from tree-shrews; i.e., Tupaia belangeri, can be substituted for primary human hepatocytes, and (2) a human hepatoma cell line (HepaRG) was established that gains susceptibility for HBV infection upon induction of differentiation in vitro. A number of potential HBV receptor candidates have been described in the past, but none of them have been confirmed to function as a receptor. For DHBV and probably all other avian hepadnaviruses, carboxypeptidase D (CPD) has been shown to be indispensable for infection, although the exact role of this molecule is still under debate. While still restricted to the use of primary duck hepatocytes (PDH), investigations performed with DHBV provided important general concepts on the first steps of hepadnaviral infection. However, with emerging data obtained from the new HBV infection systems, the hope that DHBV utilizes the same mechanism as HBV only partially held true. Nevertheless, both HBV and DHBV in vitro infection systems will help to: (1) functionally dissect the hepadnaviral entry pathways, (2) perform reverse genetics (e.g. test the fitness of escape mutants), (3) titrate and map neutralizing antibodies, (4) improve current vaccines to combat acute and chronic infections of hepatitis B, and (5) develop entry inhibitors for future clinical applications.

Molecular mechanism of pathogenesis of dengue virus: Entry and fusion with target cell

Dengue fever is one of the major health problems in India. Interaction with specific receptor(s) at the cell surface is one of the first events in the pathogenesis of Dengue virus. However, relatively little is known about these receptors. Cellular receptors in human monocytes and mouse neural cells are main target for the viral infection. The envelope protein of the virus (E-protein) plays important role in attachment of virus to target cells and their interaction with cellular receptors. The modulation of receptor gene(s) and/or protein(s) can be used as a method for interfering with virus entry and can thus become a new method for disease prevention. The receptors can be purified by affinity chromatography using E-protein as ligand. It has been reported that addition of highly sulfated heparan sulfate prevents E-protein binding to target cells suggesting that heparan sulfate is utilized by dengue envelope protein to bind to target cells.