Sulfated Escherichia coli K5 polysaccharide derivatives inhibit dengue virus infection of human microvascular endothelial cells by interacting with the viral envelope protein E domain III.

Dengue virus (DENV) is an emerging mosquito-borne pathogen that causes cytokine-mediated alterations in the barrier function of the microvascular endothelium, leading to dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS). We observed that DENV (serotype 2) productively infects primary (HMVEC-d) and immortalized (HMEC-1) human dermal microvascular endothelial cells, despite the absence of well-described DENV receptors, such as dendritic cell-specific intercellular adhesion molecule-3-grabbing non-integrin (DC-SIGN) or the mannose receptor on the cell surface. However, heparan sulfate proteoglycans (HSPGs) were highly expressed on these cells and pre-treatment of HMEC-1 cells with heparinase II or with glycosaminoglycans reduced DENV infectivity up to 90%, suggesting that DENV uses HSPGs as attachment receptor on microvascular endothelial cells. Sulfated Escherichia coli K5 derivatives, which are structurally similar to heparin/heparan sulfate but lack anticoagulant activity, were able to block DENV infection of HMEC-1 and HMVEC-d cells in the nanomolar range. The highly sulfated K5-OS(H) and K5-N,OS(H) inhibited virus attachment and subsequent entry into microvascular endothelial cells by interacting with the viral envelope (E) protein, as shown by surface plasmon resonance (SPR) analysis using the receptor-binding domain III of the E protein.

Crucial role of the N-glycans on the viral E-envelope glycoprotein in DC-SIGN-mediated dengue virus infection.

We generated in the mosquito cell line C6/36 a dengue virus (DENV) resistant to Hippeastrum hybrid agglutinin (HHA), a carbohydrate-binding agent (CBA). The genotype and phenotype were characterized of the HHA resistant (HHA(res)) DENV compared to the wild-type (WT) DENV. Sequencing the structural proteins of HHA(res) resulted in two mutations, N67D and T155I, indicating a deletion of both N-glycosylation sites on the viral envelope E-glycoprotein. The HHA(res) DENV could replicate in mammalian and mosquito cells that are lacking dendritic cell-specific intercellular adhesion molecule 3-grabbing non-integrin (DC-SIGN) expression. In contrast, DC-SIGN expressing human cells namely monocyte-derived dendritic cells as well as DC-SIGN-transfected cells were no longer susceptible to HHA(res) DENV. This demonstrates a crucial role of the N-glycans in the E-glycoprotein in the infection of dendritic cells, which constitute primary target cells of DENV during viral pathogenesis in the human body.

Dengue virus entry as target for antiviral therapy.

Dengue virus (DENV) infections are expanding worldwide and, because of the lack of a vaccine, the search for antiviral products is imperative. Four serotypes of DENV are described and they all cause a similar disease outcome. It would be interesting to develop an antiviral product that can interact with all four serotypes, prevent host cell infection and subsequent immune activation. DENV entry is thus an interesting target for antiviral therapy. DENV enters the host cell through receptor-mediated endocytosis. Several cellular receptors have been proposed, and DC-SIGN, present on dendritic cells, is considered as the most important DENV receptor until now. Because DENV entry is a target for antiviral therapy, various classes of compounds have been investigated to inhibit this process. In this paper, an overview is given of all the putative DENV receptors, and the most promising DENV entry inhibitors are discussed.

Broad antiviral activity of carbohydrate-binding agents against the four serotypes of dengue virus in monocyte-derived dendritic cells.

BACKGROUND: Dendritic cells (DC), present in the skin, are the first target cells of dengue virus (DENV). Dendritic cell-specific intercellular adhesion molecule 3-grabbing non-integrin (DC-SIGN) is present on DC and recognizes N-glycosylation sites on the E-glycoprotein of DENV. Thus, the DC-SIGN/E-glycoprotein interaction can be considered as an important target for inhibitors of viral replication. We evaluated various carbohydrate-binding agents (CBAs) against all four described serotypes of DENV replication in Raji/DC-SIGN(+) cells and in monocyte-derived DC (MDDC). METHODOLOGY/PRINCIPAL FINDINGS: A dose-dependent anti-DENV activity of the CBAs Hippeastrum hybrid (HHA), Galanthus nivalis (GNA) and Urtica dioica (UDA), but not actinohivin (AH) was observed against all four DENV serotypes as analyzed by flow cytometry making use of anti-DENV antibodies. Remarkably, the potency of the CBAs against DENV in MDDC cultures was significantly higher (up to 100-fold) than in Raji/DC-SIGN(+) cells. Pradimicin-S (PRM-S), a small-size non-peptidic CBA, exerted antiviral activity in MDDC but not in Raji/DC-SIGN(+) cells. The CBAs act at an early step of DENV infection as they bind to the viral envelope of DENV and subsequently prevent virus attachment. Only weak antiviral activity of the CBAs was detected when administered after the virus attachment step. The CBAs were also able to completely prevent the cellular activation and differentiation process of MDDC induced upon DENV infection. CONCLUSIONS/SIGNIFICANCE: The CBAs exerted broad spectrum antiviral activity against the four DENV serotypes, laboratory-adapted viruses and low passage clinical isolates, evaluated in Raji/DC-SIGN(+) cells and in primary MDDC.

A derivate of the antibiotic doxorubicin is a selective inhibitor of dengue and yellow fever virus replication in vitro.

A doxorubicin derivate, SA-17, that carries a squaric acid amide ester moiety at the carbohydrate (α-l-daunosaminyl) group was identified as a selective inhibitor of in vitro dengue virus (DENV) serotype 2 replication (50% effective concentration [EC(50)] = 0.34 ± 0.20 µg/ml [0.52 ± 0.31 µM]). SA-17 is markedly less cytostatic than the parent compound, resulting in a selectivity index value of ∼100. SA-17 also inhibits yellow fever virus 17D (YFV-17D) replication (EC(50) = 3.1 ± 1.0 µg/ml [4.8 ± 1.5 µM]), although less efficiently than DENV replication, but proved inactive against a variety of enveloped and nonenveloped viruses. SA-17 inhibits in vitro flavivirus replication in a dose-dependent manner, as was assessed by virus yield reduction assays and quantification of viral RNA by means of real-time quantitative reverse transcriptase PCR (RT-qPCR) (∼2 to 3 log reduction). The anti-DENV activity was confirmed using a Renilla luciferase-expressing dengue reporter virus. Time-of-drug-addition studies revealed that SA-17 acts at the very early stages of the viral replication cycle (i.e., virus attachment and/or virus entry). This observation was corroborated by the observation that SA-17, unlike the nucleoside analogue ribavirin, does not inhibit the replication of DENV subgenomic replicons. Preincubation of high-titer stocks of DENV or YFV-17D with ≥5 µg/ml SA-17 resulted in 100% inhibition of viral infectivity (≥3 log reduction). SA-17, however, did not prove virucidal.

Antiviral activity of carbohydrate-binding agents and the role of DC-SIGN in dengue virus infection.

Dendritic cell-specific intercellular adhesion molecule 3-grabbing non-integrin (DC-SIGN) is an important binding receptor for dengue virus (DENV) that recognizes N-glycosylation sites on the viral E-glycoprotein. DENV cannot bind nor infect the human B-cell line Raji/0. However, DENV productively infects Raji/DC-SIGN(+) cells that constitutively express DC-SIGN on their surface. IL-4-treated monocytes, expressing high levels of DC-SIGN, are also susceptible for DENV infection. Several carbohydrate-binding agents (CBAs), such as the plant lectins HHA, GNA (mannose-specific) and UDA (N-acetylglucosamine-specific), inhibited dose-dependently the binding of DENV and subsequently viral replication in Raji/DC-SIGN(+) cells (EC(50): 0.1-2.2 microM). These CBAs were clearly more active against DENV in IL-4-treated monocytes (EC(50): 4-56 nM). However, the CBAs were devoid of antiviral activity in DENV-susceptible Vero-B (DC-SIGN(-)) cells, demonstrating cell type-dependent differences in viral entry mechanisms.

Protective role of IFN-gamma in collagen-induced arthritis conferred by inhibition of mycobacteria-induced granulocyte chemotactic protein-2 production.

Mice with a disrupted IFN-gamma system are remarkably susceptible to experimental autoimmune diseases, such as collagen-induced arthritis (CIA), which rely on the use of CFA. The inflammatory lesions of these IFN-gamma knockout (KO) mice are characterized by an excessive proportion of neutrophils. Here, we show that the increased severity of CIA in IFN-gammaR KO as compared with wild-type mice is accompanied by increased levels of the CXC chemokine granulocyte chemotactic protein-2 (GCP-2), a major neutrophil-attracting chemokine in mice. We demonstrated that the heat-killed mycobacteria present in CFA elicited production of GCP-2 in mouse embryo fibroblast cultures and that this production was inhibited by IFN-gamma. Inhibition of GCP-2 production by IFN-gamma was STAT-1-dependent. IFN-gamma receptor KO mice treated with neutralizing anti-GCP-2 antibodies were protected from CIA, indicating the in vivo importance of GCP-2 in the pathogenesis of CIA. Our data support the notion that one of the mechanisms whereby endogenous IFN-gamma mitigates the manifestations of CIA consists of inhibiting production of GCP-2, thereby limiting mobilization and infiltration of neutrophils, which are important actors in joint inflammation. These results may also be applicable to other experimental models of autoimmunity that rely on the use of CFA.