Dihydromyricetin inhibits African swine fever virus replication by downregulating toll-like receptor 4-dependent pyroptosis in vitro

African swine fever (ASF), caused by ASF virus (ASFV) infection, poses a huge threat to the pork industry owing to ineffective preventive and control measures. Hence, there is an urgent need to develop strategies, including antiviral drugs targeting ASFV, for preventing ASFV spread. This study aimed to identify novel compounds with anti-ASFV activity. To this end, we screened a small chemical library of 102 compounds, among which the natural flavonoid dihydromyricetin (DHM) exhibited the most potent anti-ASFV activity. DHM treatment inhibited ASFV replication in a dose- and time-dependent manner. Furthermore, it inhibited porcine reproductive and respiratory syndrome virus and swine influenza virus replication, which suggested that DHM exerts broad-spectrum antiviral effects. Mechanistically, DHM treatment inhibited ASFV replication in various ways in the time-to-addition assay, including pre-, co-, and post-treatment. Moreover, DHM treatment reduced the levels of ASFV-induced inflammatory mediators by regulating the TLR4/MyD88/MAPK/NF-κB signaling pathway. Meanwhile, DHM treatment reduced the ASFV-induced accumulation of reactive oxygen species, further minimizing pyroptosis by inhibiting the ASFV-induced NLRP3 inflammasome activation. Interestingly, the effects of DHM on ASFV were partly reversed by treatment with polyphyllin VI (a pyroptosis agonist) and RS 09 TFA (a TLR4 agonist), suggesting that DHM inhibits pyroptosis by regulating TLR4 signaling. Furthermore, targeting TLR4 with resatorvid (a specific inhibitor of TLR4) and small interfering RNA against TLR4 impaired ASFV replication. Taken together, these results reveal the anti-ASFV activity of DHM and the underlying mechanism of action, providing a potential compound for developing antiviral drugs targeting ASFV.

Artesunate inhibits PDE4 leading to intracellular cAMP accumulation, reduced ERK/MAPK signaling, and blockade of influenza A virus vRNP nuclear export

Influenza A viruses (IAV) have been a major cause of mortality. Given the potential for future deadly pandemics, effective drugs are needed for the treatment of severe influenzas, such as those caused by H5N1 IAV. The anti-malaria drugs artemisinin and its derivates, including artesunate (AS), have been reported to have broad antiviral activities. Here, we showed AS's antiviral activity against H5N1, H1N1, H3N2 and oseltamivir-resistant influenza A(H1N1)virus in vitro. Moreover, we showed that AS treatment significantly protected mice from lethal challenges with H1N1 and H5N1 IAV. Strikingly, the combination of AS and peramivir treatment significantly improved survival outcomes compared to their monotherapy with either AS or peramivir. Furthermore, we demonstrated mechanistically that AS affected the later stages of IAV replication and limited nuclear export of viral ribonucleoprotein (vRNP) complexes. In A549 cells, we demonstrated for the first time that AS treatment induced cAMP accumulation via inhibiting PDE4, and consequently reduced ERK phosphorylation and blocked IAV vRNP export, and thus suppressed IAV replication. These AS's effects were reversed by the pre-treatment with a cAMP inhibitor SQ22536. Our findings suggest that AS could serve as a novel IAV inhibitor by interfering vRNP nuclear export to prevent and treat IAV infection.

Targeting ER stress/PKA/GSK-3β/β-catenin pathway as a potential novel strategy for hepatitis C virus-infected patients

BACKGROUND

Chronic hepatitis C virus (HCV) infection causes hepatocellular carcinoma (HCC). The HCC risk, while decreased compared with active HCV infection, persists in HCV-cured patients by direct-acting antiviral agents (DAA). We previously demonstrated that Wnt/β-catenin signaling remained activated after DAA-mediated HCV eradication. Developing therapeutic strategies to both eradicate HCV and reverse Wnt/β-catenin signaling is needed.

METHODS

Cell-based HCV long term infection was established. Chronically HCV infected cells were treated with DAA, protein kinase A (PKA) inhibitor H89 and endoplasmic reticulum (ER) stress inhibitor tauroursodeoxycholic acid (TUDCA). Western blotting analysis and fluorescence microscopy were performed to determine HCV levels and component levels involved in ER stress/PKA/glycogen synthase kinase-3β (GSK-3β)/β-catenin pathway. Meanwhile, the effects of H89 and TUDCA were determined on HCV infection.

RESULTS

Both chronic HCV infection and replicon-induced Wnt/β-catenin signaling remained activated after HCV and replicon eradication by DAA. HCV infection activated PKA activity and PKA/GSK-3β-mediated Wnt/β-catenin signaling. Inhibition of PKA with H89 both repressed HCV and replicon replication and reversed PKA/GSK-3β-mediated Wnt/β-catenin signaling in both chronic HCV infection and replicon. Both chronic HCV infection and replicon induced ER stress. Inhibition of ER stress with TUDCA both repressed HCV and replicon replication and reversed ER stress/PKA/GSK-3β-dependent Wnt/β-catenin signaling. Inhibition of either PKA or ER stress both inhibited extracellular HCV infection.

CONCLUSION

Targeting ER stress/PKA/GSK-3β-dependent Wnt/β-catenin signaling with PKA inhibitor could be a novel therapeutic strategy for HCV-infected patients to overcomes the issue of remaining activated Wnt/β-catenin signaling by DAA treatment. Video Abstract.

MEK inhibitors as novel host-targeted antivirals with a dual-benefit mode of action against hyperinflammatory respiratory viral diseases

Acute hyperinflammatory virus infections, such as influenza or coronavirus disease-19, are still a major health burden worldwide. In these diseases, a massive overproduction of pro-inflammatory cytokines and chemokines (cytokine storm syndrome) determine the severity of the disease, especially in late stages. Direct-acting antivirals against these pathogens have to be administered very early after infection to be effective and may induce viral resistance. Here, we summarize data on a host-targeted strategy using inhibitors of the cellular Raf/MEK/ERK kinase cascade that not only block replication of different RNA viruses but also suppress the hyperinflammatory cytokine response upon infection. In the first phase-II clinical trial of that approach, the MEK inhibitor Zapnometinib shows evidence of clinical benefit.

Research progress on the effect of traditional Chinese medicine on the activation of PRRs-mediated NF-κB signaling pathway to inhibit influenza pneumonia

Influenza pneumonia has challenged public health and social development. One of the hallmarks of severe influenza pneumonia is overproduction of pro-inflammatory cytokines and chemokines, which result from the continuous activation of intracellular signaling pathways, such as the NF-κB pathway, mediated by the interplay between viruses and host pattern recognition receptors (PRRs). It has been reported that traditional Chinese medicines (TCMs) can not only inhibit viral replication and inflammatory responses but also affect the expression of key components of PRRs and NF-κB signaling pathways. However, whether the antiviral and anti-inflammatory roles of TCM are related with its effects on NF-κB signaling pathway activated by PRRs remains unclear. Here, we reviewed the mechanism of PRRs-mediated activation of NF-κB signaling pathway following influenza virus infection and summarized the influence of anti-influenza TCMs on inflammatory responses and the PRRs/NF-κB signaling pathway, so as to provide better understanding of the mode of action of TCMs in the treatment of influenza pneumonia.

Pharmacokinetics, absorption, distribution, metabolism and excretion of the MEK inhibitor zapnometinib in rats

Zapnometinib is a MEK inhibitor currently under clinical development for the treatment of COVID-19 and influenza. Zapnometinib has both antiviral and immunomodulatory effects. Information concerning the absorption, distribution, metabolism, and excretion of the compound following single oral doses of 30 mg/kg [¹⁴C]-zapnometinib to rats was required to support pharmacology and toxicology studies in animals and clinical studies in man. As part of the development and safety assessment of this substance, zapnometinib was radioactively labeled and used for the investigation of time-dependent plasma concentrations, the rates and routes of excretion, the extent and time-course of compound distribution in body tissues, the metabolite profiles in plasma, urine and feces and the chemical nature of its metabolites. The present study reveals a rapid but low absorption of zapnometinib from the gastrointestinal tract, with more than 90% of the compound being excreted within 48 h, mainly via feces. Whole body autoradiography confirms that zapnometinib was rapidly and widely distributed, with greatest concentrations in the circulatory and visceral tissues. Maximum plasma and tissue concentrations occurred between two and 8 h post dose. Penetration into the brain was low, and elimination from most tissues almost complete after 168 h. Metabolic profiles showed that the main clearance routes were metabolism via oxidative reactions and glucuronidation. These results further strengthen the knowledge of zapnometinib with respect to the clinical development of the drug.

FDA-Approved Inhibitors of RTK/Raf Signaling Potently Impair Multiple Steps of In Vitro and Ex Vivo Influenza A Virus Infections

Influenza virus (IV) infections pose a burden on global public health with significant morbidity and mortality. The limited range of currently licensed IV antiviral drugs is susceptible to the rapid rise of resistant viruses. In contrast, FDA-approved kinase inhibitors can be repurposed as fast-tracked host-targeted antivirals with a higher barrier of resistance. Extending our recent studies, we screened 21 FDA-approved small-molecule kinase inhibitors (SMKIs) and identified seven candidates as potent inhibitors of pandemic and seasonal IV infections. These SMKIs were further validated in a biologically and clinically relevant ex vivo model of human precision-cut lung slices. We identified steps of the virus infection cycle affected by these inhibitors (entry, replication, egress) and found that most SMKIs affected both entry and egress. Based on defined and overlapping targets of these inhibitors, the candidate SMKIs target receptor tyrosine kinase (RTK)-mediated activation of Raf/MEK/ERK pathways to limit influenza A virus infection. Our data and the established safety profiles of these SMKIs support further clinical investigations and repurposing of these SMKIs as host-targeted influenza therapeutics.

Broadly Applicable, Virus-Free Dual Reporter Assay to Identify Compounds Interfering with Membrane Fusion: Performance for HSV-1 and SARS-CoV-2

Membrane fusion constitutes an essential step in the replication cycle of numerous viral pathogens, hence it represents an important druggable target. In the present study, we established a virus-free, stable reporter fusion inhibition assay (SRFIA) specifically designed to identify compounds interfering with virus-induced membrane fusion. The dual reporter assay is based on two stable Vero cell lines harboring the third-generation tetracycline (Tet3G) transactivator and a bicistronic reporter gene cassette under the control of the tetracycline responsive element (TRE3G), respectively. Cell–cell fusion by the transient transfection of viral fusogens in the presence of doxycycline results in the expression of the reporter enzyme secreted alkaline phosphatase (SEAP) and the fluorescent nuclear localization marker EYFPNuc. A constitutively expressed, secreted form of nanoluciferase (secNLuc) functioned as the internal control. The performance of the SRFIA was tested for the quantification of SARS-CoV-2- and HSV-1-induced cell–cell fusion, respectively, showing high sensitivity and specificity, as well as the reliable identification of known fusion inhibitors. Parallel quantification of secNLuc enabled the detection of cytotoxic compounds or insufficient transfection efficacy. In conclusion, the SRFIA reported here is well suited for high-throughput screening for new antiviral agents and essentially will be applicable to all viral fusogens causing cell–cell fusion in Vero cells.

Pharmacokinetics, Pharmacodynamics and Antiviral Efficacy of the MEK Inhibitor Zapnometinib in Animal Models and in Humans

The mitogen-activated protein kinase (MEK) inhibitor zapnometinib is in development to treat acute viral infections like COVID-19 and influenza. While the antiviral efficacy of zapnometinib is well documented, further data on target engagement/pharmacodynamics (PD) and pharmacokinetics (PK) are needed. Here, we report zapnometinib PK and PD parameters in mice, hamsters, dogs, and healthy human volunteers. Mice received 25 mg/kg/day zapnometinib (12.5 mg/kg p. o. twice daily, 8 h interval). Syrian hamsters received 30 mg/kg (15 mg/kg twice daily) or 60 mg/kg/day once daily. Beagle dogs were administered 300 mg/kg/day, and healthy human volunteers were administered 100, 300, 600 and 900 mg zapnometinib (once daily p. o.). Regardless of species or formulation, zapnometinib maximum plasma concentration (C_max) was reached between 2–4 h after administration with an elimination half-life of 4–5 h in dogs, 8 h in mice or hamsters and 19 h in human subjects. Doses were sufficient to cause up to 80% MEK inhibition. Across all species approximately 10 μg/ml zapnometinib was appropriate to inhibit 50% of peripheral blood mononuclear cells (PBMC) MEK activity. In mice, a 50%–80% reduction of MEK activity was sufficient to reduce influenza virus titer in the lungs by more than 90%. In general, while >50% MEK inhibition was reached in vivo at most doses, 80% inhibition in PBMCs required significantly higher doses and appeared to be the practical maximal level obtained in vivo. However, the period of reduced phosphorylated extracellular-signal regulated kinase (pERK), a measure of MEK inhibition, was maintained even after elimination of zapnometinib from plasma, suggesting a sustained effect on MEK consistent with regulatory effects or a slow off-rate. These data suggest a target plasma C_max of at least 10 μg/ml zapnometinib in further clinical studies.

Multivalent peptide dendrimers inhibit the fusion of viral-cellular membranes and the cellular NF-κB signaling pathway

The binding of the influenza A virus (IAV) to host cells is multivalent interactions between the hemagglutinin (HA) trimer and sialic acid residues on the cell surface, which present a challenge for the development of efficient antiviral drugs interfering with the entry of IAV into host cells. In this study, a number of multivalent peptide dendrimers targeting the HA2 subunit of HA to block the fusion between viral-cellular membranes have been created, of which FMOC-4-KKWK showed the lowest cytotoxicity, while in the nanomolar concentration range of antiviral effects. In addition to being active against a panel of various subtypes of influenza viruses, these dendrimers reduced the levels of NF-κB in RAW 264.7 cells and inhibited the overexpression of proinflammatory cytokines of TNF-α, IL-1β, and IL-6 that are associated with the influenza infection. Further tests in mice infected with a lethal dose of PR8 virus showed that these dendrimers increased the survival rate of mice, and reduced the viral load in the lungs. Significantly, this is the first report describing peptide dendrimers that target the HA2 subunit of IAV, differing from those using carbohydrates as ligands to block the adsorption of viruses to host cells.

Neutrophil-to-lymphocyte ratio as a potential biomarker in predicting influenza susceptibility

BACKGROUND

Human population exposed to influenza viruses exhibited wide variation in susceptibility. The ratio of neutrophils to lymphocytes (NLR) has been examined to be a marker of systemic inflammation. We sought to investigate the relationship between influenza susceptibility and the NLR taken before influenza virus infection.

METHODS

We investigated blood samples from five independent influenza challenge cohorts prior to influenza inoculation at the cellular level by using digital cytometry. We used multi-cohort gene expression analysis to compare the NLR between the symptomatic infected (SI) and asymptomatic uninfected (AU) subjects. We then used a network analysis approach to identify host factors associated with NLR and influenza susceptibility.

RESULTS

The baseline NLR was significantly higher in the SI group in both discovery and validation cohorts. The NLR achieved an AUC of 0.724 on the H3N2 data, and 0.736 on the H1N1 data in predicting influenza susceptibility. We identified four key modules that were not only significantly correlated with the baseline NLR, but also differentially expressed between the SI and AU groups. Genes within these four modules were enriched in pathways involved in B cell-mediated immune responses, cellular metabolism, cell cycle, and signal transduction, respectively.

CONCLUSIONS

This study identified the NLR as a potential biomarker for predicting disease susceptibility to symptomatic influenza. An elevated NLR was detected in susceptible hosts, who may have defects in B cell-mediated immunity or impaired function in cellular metabolism, cell cycle or signal transduction. Our work can serve as a comparative model to provide insights into the COVID-19 susceptibility.

Phosphorylation of JIP4 at S730 Presents Antiviral Properties against Influenza A Virus Infection

Influenza A virus (IAV) is the causative agent of flu disease that results in annual epidemics and occasional pandemics. IAV alters several signaling pathways of the cellular host response in order to promote its replication. Therefore, some of these pathways can serve as targets for novel antiviral agents. Here, we show that c-Jun NH2-terminal kinase (JNK)-interacting protein 4 (JIP4) is dynamically phosphorylated in IAV infection. The lack of JIP4 resulted in higher virus titers, with significant differences in viral protein and mRNA accumulation as early as within the first replication cycle. In accordance, decreased IAV titers and protein accumulation were observed during the overexpression of JIP4. Strikingly, the antiviral function of JIP4 does not originate from modulation of JNK or p38 mitogen-activated protein kinase (MAPK) pathways or from altered expression of interferons or interferon-stimulated genes but rather originates from a direct reduction of viral polymerase activity. Furthermore, the interference of JIP4 with IAV replication seems to be linked to the phosphorylation of the serine at position 730 that is sufficient to impede the viral polymerase. Collectively, we provide evidence that JIP4, a host protein modulated in IAV infection, exhibits antiviral properties that are dynamically controlled by its phosphorylation at S730. IMPORTANCE Influenza A virus (IAV) infection is a world health concern, and current treatment options encounter high rates of resistance. Our group investigates host pathways modified in IAV infection as promising new targets. The host protein JIP4 is dynamically phosphorylated in IAV infection. JIP4 absence resulted in higher virus titers and viral protein and mRNA accumulation within the first replication cycle. Accordingly, decreased IAV titers and protein accumulation were observed during JIP4 overexpression. Strikingly, the antiviral function of JIP4 does not originate from modulation of JNK or p38 MAPK pathways or from altered expression of interferons or interferon-stimulated genes but rather originates from a reduction in viral polymerase activity. The interference of JIP4 with IAV replication is linked to the phosphorylation of serine 730. We provide evidence that JIP4, a host protein modulated in IAV infection, exhibits antiviral properties that are dynamically controlled by its phosphorylation at S730.

[Identification of a metabolic immune regulator in the host that protects against influenzal pneumonia]

The 'flu, caused mostly by influenza A and B viruses, represents a major public health issue. Despite vaccines and antiviral drugs, the therapeutic arsenal is still suboptimal. Recently, several studies have reported the antiviral and anti-inflammatory properties of several host metabolites. Now, we show that a metabolite (called here "C2") has a potent anti-influenza activity by blocking the viral replication and by limiting the downstream pro-inflammatory signalling. These results pave the way for the development of innovative metabolic therapy against influenzal pneumonia.

The Two Sides of the Same Coin-Influenza Virus and Intracellular Signal Transduction

Cells respond to extracellular agents by activation of intracellular signaling pathways. Viruses can be regarded as such agents, leading to a firework of signaling inside the cell, primarily induced by pathogen-associated molecular patterns (PAMPs) that provoke safeguard mechanisms to defend from the invader. In the constant arms race between pathogen and cellular defense, viruses not only have evolved mechanisms to suppress or misuse supposedly antiviral signaling processes for their own benefit but also actively induce signaling to promote replication. This creates viral dependencies that may be exploited for novel strategies of antiviral intervention. Here, we will summarize the current knowledge of activation and function of influenza virus-induced signaling pathways with a focus on nuclear factor (NF)-κB signaling, mitogen-activated protein kinase cascades, and the phosphatidylinositol-3-kinase pathway. We will discuss the opportunities and drawbacks of targeting these signaling pathways for antiviral intervention.

MicroRNA-206 inhibits influenza A virus replication by targeting tankyrase 2

Due to the frequent mutations, influenza A virus (IAV) becomes resistant to anti-viral drugs targeting influenza viral proteins. There are increasing interests in anti-viral agents that target host cellular proteins required for virus replication. Tankyrase (TNKS) has poly (ADP-ribose) polymerase activity and is a negative regulator of many host proteins. The objectives of this study are to study the role of TNKS2 in IAV infection, identify the microRNAs targeting TNKS2, and to understand the mechanisms involved. We found that TNKS2 expression was elevated in human lung epithelial cells and mouse lungs during IAV infection. Knock-down of TNKS2 by RNA interference reduced viral replication. Using a computation approach and 3'-untranslation regions (3'-UTR) reporter assay, we identified miR-206 as the microRNA that targeted TNKS2. Overexpression of miR-206 reduced viral protein levels and virus production in cell culture. The effect of miR-206 on IAV replication was strain-independent. miR-206 activated JNK/c-Jun signalling, induced type I interferon expression and enhanced Stat signalling. Finally, the delivery of an adenovirus expressing miR-206 into the lung of mice challenged with IAV increased type I interferon response, suppressed viral load in the lungs and increased survival. Our results indicate that miR-206 has anti-influenza activity by targeting TNKS2 and subsequently activating the anti-viral state.

The influenza replication blocking inhibitor LASAG does not sensitize human epithelial cells for bacterial infections

Severe influenza virus (IV) infections still represent a major challenge to public health. To combat IV infections, vaccines and antiviral compounds are available. However, vaccine efficacies vary with very limited to no protection against newly emerging zoonotic IV introductions. In addition, the development of resistant virus variants against currently available antivirals can be rapidly detected, in consequence demanding the design of novel antiviral strategies. Virus supportive cellular signaling cascades, such as the NF-κB pathway, have been identified to be promising antiviral targets against IV in in vitro and in vivo studies and clinical trials. While administration of NF-κB pathway inhibiting agents, such as LASAG results in decreased IV replication, it remained unclear whether blocking of NF-κB might sensitize cells to secondary bacterial infections, which often come along with viral infections. Thus, we examined IV and Staphylococcus aureus growth during LASAG treatment. Interestingly, our data reveal that the presence of LASAG during superinfection still leads to reduced IV titers. Furthermore, the inhibition of the NF-κB pathway resulted in decreased intracellular Staphylococcus aureus loads within epithelial cells, indicating a dependency on the pathway for bacterial uptake. Unfortunately, so far it is not entirely clear if this phenomenon might be a drawback in bacterial clearance during infection.

Report of the 23rd Meeting on Signal Transduction 2019-Trends in Cancer and Infection

The annual meeting "Signal Transduction-Receptors, Mediators and Genes" of the Signal Transduction Society (STS) is an interdisciplinary conference open to all scientists sharing the common interest in elucidating the signalling pathways underlying the physiological or pathological processes in health and disease of humans, animals, plants, fungi, prokaryotes and protists. The 23rd meeting on signal transduction was held from 4-6 November 2019 in Weimar, Germany, and focused on "Trends in Cancer and Infection". As usual, keynote presentations by invited scientists introduced the respective workshops and were followed by speakers chosen from the submitted abstracts. Ample time had been reserved for discussion of the presented data during the workshops. In this report, we provide a concise summary of the various workshops and further aspects of the scientific program.

Proteasome Inhibitor PS-341 Effectively Blocks Infection by the Severe Fever with Thrombocytopenia Syndrome Virus

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging hemorrhagic fever disease caused by SFTSV, a newly discovered phlebovirus that is named after the disease. Currently, no effective vaccines or drugs are available for use against SFTSV infection, as our understanding of the viral pathogenesis is limited. Bortezomib (PS-341), a dipeptide-boronic acid analog, is the first clinically approved proteasome inhibitor for use in humans. In this study, the antiviral efficacy of PS-341 against SFTSV infection was tested in human embryonic kidney HEK293T (293T) cells. We employed four different assays to analyze the antiviral ability of PS-341 and determined that PS-341 inhibited the proliferation of SFTSV in 293T cells under various treatment conditions. Although PS-341 did not affect the virus absorption, PS-341 treatment within a non-toxic concentration range resulted in a significant reduction of progeny viral titers in infected cells. Dual-luciferase reporter assays and Western blot analysis revealed that PS-341 could reverse the SFTSV-encoded non-structural protein (NS) mediated degradation of retinoic acid-inducible gene-1 (RIG-I), thereby antagonizing the inhibitory effect of NSs on interferons and blocking virus replication. In addition, we observed that inhibition of apoptosis promotes virus replication. These results indicate that targeting of cellular interferon pathways and apoptosis during acute infection might serve as the bases of future therapeutics for the treatment of SFTSV infections.

Erucic acid from Isatis indigotica Fort. suppresses influenza A virus replication and inflammation in vitro and in vivo through modulation of NF-κB and p38 MAPK pathway

Isatis indigotica Fort. (Ban-Lan-Gen) is an herbal medicine prescribed for influenza treatment. However, its active components and mode of action remain mostly unknown. In the present study, erucic acid was isolated from Isatis indigotica Fort., and subsequently its underlying mechanism against influenza A virus (IAV) infection was investigated in vitro and in vivo. Our results demonstrated that erucic acid exhibited broad-spectrum antiviral activity against IAV resulting from reduction of viral polymerase transcription activity. Erucic acid was found to exert inhibitory effects on IAV or viral (v) RNA-induced pro-inflammatory mediators as well as interferons (IFNs). The molecular mechanism by which erucic acid with antiviral and anti-inflammatory properties was attributed to inactivation of NF-κB and p38 MAPK signaling. Furthermore, the NF-κB and p38 MAPK inhibitory effect of erucic acid led to diminishing the transcriptional activity of interferon-stimulated gene factor 3 (ISGF-3), and thereby reducing IAV-triggered pro-inflammatory response amplification in IFN-β-sensitized cells. Additionally, IAV- or vRNA-triggered apoptosis of alveolar epithelial A549 cells was prevented by erucic acid. In vivo, erucic acid administration consistently displayed decreased lung viral load and viral antigens expression. Meanwhile, erucic acid markedly reduced CD8⁺ cytotoxic T lymphocyte (CTL) recruitment, pro-apoptotic signaling, hyperactivity of multiple signaling pathways, and exacerbated immune inflammation in the lung, which resulted in decreased lung injury and mortality in mice with a mouse-adapted A/FM/1/47-MA(H1N1) strain infection. Our findings provided a mechanistic basis for the action of erucic acid against IAV-mediated inflammation and injury, suggesting that erucic acid may have a therapeutic potential in the treatment of influenza.

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Erucic acid from Isatis indigotica Fort. exhibited broad-spectrum anti-influenza virus activity.

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Erucic acid reduced IAV polymerase transcription activity.

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Erucic acid suppressed IAV-triggered inflammation as well as pro-inflammatory amplification effects in IFN-sensitized cells.

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Erucic acid protected mice from lethal IAV infection.

p-STAT1 regulates the influenza A virus replication and inflammatory response in vitro and vivo

Influenza A virus infection activates various intracellular signaling pathways, which is mediated by the transcription factors. Here, a quantitative phosphoproteomic analysis of A549 cells after infection with influenza A virus (H5N1) was performed and we found that the transcription factor STAT1 was highly activated. Unexpectedly, upon inhibition of p-STAT1, titers of progeny virus and viral protein synthesis were both reduced. The STAT1 inhibitor Fludarabine (FLUD) inhibited an early progeny step in viral infection and reduced the levels of influenza virus genomic RNA (vRNA). Concomitantly, there was reduced expression of inflammatory cytokines in p-STAT1 inhibited cells. In vivo, suppression of p-STAT1 improved the survival of H5N1 virus-infected mice, reduced the pulmonary inflammatory response and viral burden. Thus, our data demonstrated a critical role for p-STAT1 in influenza virus replication and inflammatory responses. We speculate that STAT1 is an example of a putative antiviral signaling component to support effective replication.

Phosphoproteome Analysis of Cells Infected with Adapted and Nonadapted Influenza A Virus Reveals Novel Pro- and Antiviral Signaling Networks

Influenza A viruses (IAVs) quickly adapt to new environments and are well known to cross species barriers. To reveal a molecular basis for these phenomena, we compared the Ser/Thr and Tyr phosphoproteomes of murine lung epithelial cells early and late after infection with mouse-adapted SC35M virus or its nonadapted SC35 counterpart. With this analysis we identified a large set of upregulated Ser/Thr phosphorylations common to both viral genotypes, while Tyr phosphorylations showed little overlap. Most of the proteins undergoing massive changes of phosphorylation in response to both viruses regulate chromatin structure, RNA metabolism, and cell adhesion, including a focal adhesion kinase (FAK)-regulated network mediating the regulation of actin dynamics. IAV also affected phosphorylation of activation loops of 37 protein kinases, including FAK and several phosphatases, many of which were not previously implicated in influenza virus infection. Inhibition of FAK proved its contribution to IAV infection. Novel phosphorylation sites were found on IAV-encoded proteins, and the functional analysis of selected phosphorylation sites showed that they either support (NA Ser178) or inhibit (PB1 Thr223) virus propagation. Together, these data allow novel insights into IAV-triggered regulatory phosphorylation circuits and signaling networks.IMPORTANCE Infection with IAVs leads to the induction of complex signaling cascades, which apparently serve two opposing functions. On the one hand, the virus highjacks cellular signaling cascades in order to support its propagation; on the other hand, the host cell triggers antiviral signaling networks. Here we focused on IAV-triggered phosphorylation events in a systematic fashion by deep sequencing of the phosphoproteomes. This study revealed a plethora of newly phosphorylated proteins. We also identified 37 protein kinases and a range of phosphatases that are activated or inactivated following IAV infection. Moreover, we identified new phosphorylation sites on IAV-encoded proteins. Some of these phosphorylations support the enzymatic function of viral components, while other phosphorylations are inhibitory, as exemplified by PB1 Thr223 modification. Our global characterization of IAV-triggered patterns of phospho-proteins provides a rich resource to further understand host responses to infection at the level of phosphorylation-dependent signaling networks.

Influenza Virus Infections and Cellular Kinases

Influenza A viruses (IAVs) are a major cause of respiratory illness and are responsible for yearly epidemics associated with more than 500,000 annual deaths globally. Novel IAVs may cause pandemic outbreaks and zoonotic infections with, for example, highly pathogenic avian influenza virus (HPAIV) of the H5N1 and H7N9 subtypes, which pose a threat to public health. Treatment options are limited and emergence of strains resistant to antiviral drugs jeopardize this even further. Like all viruses, IAVs depend on host factors for every step of the virus replication cycle. Host kinases link multiple signaling pathways in respond to a myriad of stimuli, including viral infections. Their regulation of multiple response networks has justified actively targeting cellular kinases for anti-cancer therapies and immune modulators for decades. There is a growing volume of research highlighting the significant role of cellular kinases in regulating IAV infections. Their functional role is illustrated by the required phosphorylation of several IAV proteins necessary for replication and/or evasion/suppression of the innate immune response. Identified in the majority of host factor screens, functional studies further support the important role of kinases and their potential as host restriction factors. PKC, ERK, PI3K and FAK, to name a few, are kinases that regulate viral entry and replication. Additionally, kinases such as IKK, JNK and p38 MAPK are essential in mediating viral sensor signaling cascades that regulate expression of antiviral chemokines and cytokines. The feasibility of targeting kinases is steadily moving from bench to clinic and already-approved cancer drugs could potentially be repurposed for treatments of severe IAV infections. In this review, we will focus on the contribution of cellular kinases to IAV infections and their value as potential therapeutic targets.

Antiviral potential of human IFN-α subtypes against influenza A H3N2 infection in human lung explants reveals subtype-specific activities

Influenza is an acute respiratory infection causing high morbidity and mortality in annual outbreaks worldwide. Antiviral drugs are limited and pose the risk of resistance development, calling for new treatment options. IFN-α subtypes are immune-stimulatory cytokines with strong antiviral activities against IAV in vitro and in vivo. However, the clinical use of IFN-α2, the only licensed subtype of this multi-gene family, could not prevent or limit IAV infections in humans. However, the other subtypes were not investigated.Therefore, this study evaluated the induction and antiviral potential of all human IFN-α subtypes during H3N2 IAV infection in human lung explants. We found that subtypes with weak antiviral activities were preferentially induced during IAV infection in human lungs. Intriguingly, non-induced subtypes α16, α5 and α4 suppressed viral replication up to 230-fold more efficiently than α2. Furthermore, our results demonstrate that subtypes with stronger antiviral activities induce higher expression of IAV-specific restriction factors and that MxA expression is a determinant of the subtype-specific antiviral activity towards H3N2 IAV. These results corroborate that IFN-α subtypes exhibit differential antiviral activities and emphasize that subtypes α16, α5 and α4 should be further investigated for the prevention and treatment of severe infections with seasonal H3N2 IAV.

(+)‑pinoresinol‑O‑β‑D‑glucopyranoside from Eucommia ulmoides Oliver and its anti‑inflammatory and antiviral effects against influenza A (H1N1) virus infection

Eucommia ulmoides Oliver (Du-Zhong) is an ancient Chinese herbal remedy used for the treatment of various diseases. To date, the effects of its constituent lignans on influenza viruses remain to be elucidated. In the present study, a lignan glycoside was isolated and purified from Eucommia ulmoides Oliver. Its structures were identified via extensive spectroscopic analysis, and its antiviral and anti‑inflammatory activities, specifically against influenza viruses, were determined via a cytopathic effect (CPE) assay, plaque‑reduction assays, a progeny virus yield reduction assay, reverse transcription‑quantitative polymerase chain reaction analysis and a Luminex assay. Additionally, western blot analysis was performed to investigate the underlying mechanisms of its effects against influenza viruses. The chemical and spectroscopic methods determined the structure of lignan glycoside to be (+)‑pinoresinol‑O‑β‑D‑glucopyranoside. The CPE assay showed that (+)‑pinoresinol‑O‑β‑D‑glucopyranoside exerted inhibitory activities with 50% inhibition concentration values of 408.81±5.24 and 176.24±4.41 µg/ml against the influenza A/PR/8/34 (H1N1) and A/Guangzhou/GIRD07/09 (H1N1) strains, respectively. Its antiviral properties were confirmed by plaque reduction and progeny virus yield reduction assays. Additional mechanistic analyses indicated that the anti‑H1N1 virus‑induced effects of (+)‑pinoresinol‑O-β‑D-glucopyranoside were likely due to inactivation of the nuclear factor‑κB, p38 mitogen‑activated protein kinase and AKT signaling pathways. Furthermore, (+)‑pinoresinol‑O‑β‑D‑glucopyranoside exhibited pronounced inhibitory effects on the expression of influenza H1N1 virus‑induced pro‑inflammatory mediators, including tumor necrosis factor‑α, interleukin (IL)‑6, IL‑8 and monocyte chemoattractant protein 1. The data obtained suggest that (+)‑pinoresinol‑O‑β‑D-glucopyranoside may be a candidate drug for treating influenza H1N1 virus infection.

Deep sequencing of primary human lung epithelial cells challenged with H5N1 influenza virus reveals a proviral role for CEACAM1

Current prophylactic and therapeutic strategies targeting human influenza viruses include vaccines and antivirals. Given variable rates of vaccine efficacy and antiviral resistance, alternative strategies are urgently required to improve disease outcomes. Here we describe the use of HiSeq deep sequencing to analyze host gene expression in primary human alveolar epithelial type II cells infected with highly pathogenic avian influenza H5N1 virus. At 24 hours post-infection, 623 host genes were significantly upregulated, including the cell adhesion molecule CEACAM1. H5N1 virus infection stimulated significantly higher CEACAM1 protein expression when compared to influenza A PR8 (H1N1) virus, suggesting a key role for CEACAM1 in influenza virus pathogenicity. Furthermore, silencing of endogenous CEACAM1 resulted in reduced levels of proinflammatory cytokine/chemokine production, as well as reduced levels of virus replication following H5N1 infection. Our study provides evidence for the involvement of CEACAM1 in a clinically relevant model of H5N1 infection and may assist in the development of host-oriented antiviral strategies.

Phosphoproteomic-based kinase profiling early in influenza virus infection identifies GRK2 as antiviral drug target

Although annual influenza epidemics affect around 10% of the global population, current treatment options are limited and development of new antivirals is needed. Here, using quantitative phosphoproteomics, we reveal the unique phosphoproteome dynamics that occur in the host cell within minutes of influenza A virus (IAV) infection. We uncover cellular kinases required for the observed signaling pattern and find that inhibition of selected candidates, such as the G protein-coupled receptor kinase 2 (GRK2), leads to decreased IAV replication. As GRK2 has emerged as drug target in heart disease, we focus on its role in IAV infection and show that it is required for viral uncoating. Replication of seasonal and pandemic IAVs is severely decreased by specific GRK2 inhibitors in primary human airway cultures and in mice. Our study reveals the IAV-induced changes to the cellular phosphoproteome and identifies GRK2 as crucial node of the kinase network that enables IAV replication.

Influenza A virus (IAV) causes annual epidemics and development of antivirals is needed. Here, the authors perform phosphoproteomics during IAV entry and identify GRK2 as drug target, inhibition of which decreases replication of seasonal and pandemic IAV in primary human cells and animal models.

The clinically approved MEK inhibitor Trametinib efficiently blocks influenza A virus propagation and cytokine expression

Influenza A virus (IAV) infections are still a major global threat for humans, especially for the risk groups of young children and the elderly. Annual epidemics and sporadically occurring pandemics highlight the necessity of effective antivirals that can limit viral replication. The currently licensed antiviral drugs target viral factors and are prone to provoke viral resistance. In infected host cells IAV induces various cellular signaling cascades. The Raf/MEK/ERK signaling cascade is indispensable for IAV replication because it triggers the nuclear export of newly assembled viral ribonucleoproteins (vRNPs). Inhibition of this cascade limits viral replication. Thus, next to their potential in anti-tumor therapy, inhibitors targeting the Raf/MEK/ERK signaling cascade came into focus as potential antiviral drugs. The first licensed MEK inhibitor Trametinib (GSK-1120212) is used for treatment of malignant melanoma, being highly selective and having a promising side effect profile. Since Trametinib may be qualified for a repurposing approach that would significantly shorten development time for an anti-flu use, we evaluated its antiviral potency and mode of action. In this study, we describe that Trametinib efficiently blocks replication of different IAV subtypes in vitro and in vivo. The broad antiviral activity against various IAV strains was due to its ability to interfere with export of progeny vRNPs from the nucleus. The compound also limited hyper-expression of several cytokines. Thus, we show for the first time that a clinically approved MEK inhibitor acts as a potent anti-influenza agent.

The Annexin A1 Receptor FPR2 Regulates the Endosomal Export of Influenza Virus

The Formyl Peptide Receptor 2 (FPR2) is a novel promising target for the treatment of influenza. During viral infection, FPR2 is activated by annexinA1, which is present in the envelope of influenza viruses; this activation promotes virus replication. Here, we investigated whether blockage of FPR2 would affect the genome trafficking of influenza virus. We found that, upon infection and cell treatment with the specific FPR2 antagonist WRW4 or the anti-FPR2 monoclonal antibody, FN-1D6-AI, influenza viruses were blocked into endosomes. This effect was independent on the strain and was observed for H1N1 and H3N2 viruses. In addition, blocking FPR2signaling in alveolar lung A549 epithelial cells with the monoclonal anti-FPR2 antibody significantly inhibited virus replication. Altogether, these results show that FPR2signaling interferes with the endosomal trafficking of influenza viruses and provides, for the first time, the proof of concept that monoclonal antibodies directed against FPR2 inhibit virus replication. Antibodies-based therapeutics have emerged as attractive reagents in infectious diseases. Thus, this study suggests that the use of anti-FPR2 antibodies against influenza hold great promise for the future.

Vemurafenib Limits Influenza A Virus Propagation by Targeting Multiple Signaling Pathways

Influenza A viruses (IAV) can cause severe global pandemic outbreaks. The currently licensed antiviral drugs are not very effective and prone to viral resistance. Thus, novel effective and broadly active drugs are urgently needed. We have identified the cellular Raf/MEK/ERK signaling cascade as crucial for IAV replication and suitable target for an antiviral intervention. Since this signaling cascade is aberrantly activated in many human cancers, several clinically approved inhibitors of Raf and MEK are now available. Here we explored the anti-IAV action of the licensed B-RafV600E inhibitor Vemurafenib. Treatment of B-RafWT cells with Vemurafenib induced a hyperactivation of the Raf/MEK/ERK cascade rather than inhibiting its activation upon IAV infection. Despite this hyperactivation, which has also been confirmed by others, Vemurafenib still strongly limited IAV-induced activation of other signaling cascades especially of p38 and JNK mitogen-activated protein kinase (MAPK) pathways. Most interestingly, Vemurafenib inhibited virus-induced apoptosis via impaired expression of apoptosis-inducing cytokines and led to hampered viral protein expression most likely due to the decreased activation of p38 and JNK MAPK. These multiple actions resulted in a profound and broadly active inhibition of viral replication, up to a titer reduction of three orders of a magnitude. Thus, while Vemurafenib did not act similar to MEK inhibitors, it displays strong antiviral properties via a distinct and multi-target mode of action.

Anti-inflammatory and antiviral activities of cynanversicoside A and cynanversicoside C isolated from Cynanchun paniculatum in influenza A virus-infected mice pulmonary microvascular endothelial cells

BACKGROUND

Outbreaks of the influenza A virus (IAV) often occur in various avian and mammalian species, including humans, causing serious respiratory injury worldwide. Therapeutic actions are limited to vaccines and a few antiviral drugs. Combination antiviral compounds and anti-inflammatory modulators to control the propagation of viruses would be more efficient therapeutic strategies for infectious diseases.

PURPOSE

This study was designed to isolate anti-inflammatory and antiviral compounds from Cynanchun paniculatum and elucidate their potential molecular mechanisms.

METHODS/STUDY DESIGNS

Bioactivity-guided isolation (via in vitro anti-inflammatory assay) was performed on the ethanolic extract of C. paniculatum, the structures of active compounds were elucidated by comparing spectral data (ESI-MS, ¹H NMR and ¹³C NMR) with literature values. The antiviral activity of active compounds against Influenza A virus (IAV) was determined using the cytopathic effect (CPE) inhibition assay. Inhibitory effects of active compounds on influenza A/FM1/1/47 (H1N1) virus infection were also determined by RT-PCR. Effect of active compounds on NF-kB and MAPK signaling pathways after virus infection was determined by ELISA.

RESULTS

Two compounds that showed great anti-inflammatory activity were isolated from C. paniculatum and elucidated as cynanversicoside A and cynanversicoside C. Cytokine assay demonstrated that cynanversicoside A and cynanversicoside C can suppress the production of TNF-α, IL-6 and IL-1β in Mice Pulmonary Microvascular Endothelial Cells (MPMEC) after Influenza virus A/FM/1/47 infection (p < .05) and also decreased the expressions of p-p65 and p-IκBα in infected cells. Furthermore, the phosphorylation of p38, ERK and JNK was also significantly attenuated. Subsequently, cynanversicoside A and cynanversicoside C treatment resulted in decreased viral replication and viral mRNA synthesis.

CONCLUSIONS

These results indicate that cynanversicoside A isolated from C. paniculatum has potent anti-inflammatory and antiviral effects on IAV-infected MPMEC by the regulation of NF-κB and MAPK signaling pathways.

Intranasal co-administration of 1,8-cineole with influenza vaccine provide cross-protection against influenza virus infection

BACKGROUND

Vaccination is the most efficient means for protection against influenza. However, the various vaccines have low efficacy to protect against pandemic strains because of antigenic drift and recombination of influenza virus. Adjuvant therapy is one of the attempts to improve influenza vaccine effective cross-protection against influenza virus infection. Our previous study confirmed that 1,8-cineole inhibits the NF-κB, reduces pro-inflammatory cytokines, and relieves the pathological changes of viral pneumonia in mice infected with influenza virus.

HYPOTHESIS/PURPOSE

1,8-cineole, administered via intranasal (i.n.) route, may also have the capacity to be an adjuvant of the influenza vaccine. This study was designed to investigate the potential use of i.n. co-administration of 1,8-cineole, a major component of the Eucalyptus essential oils, with influenza vaccine and whether could provide cross-protection against influenza virus infection in a mouse model.

STUDY DESIGN

I.n. co-administration of 1,8-cineole in two doses (6.25 and 12.5 mg/kg) with influenza vaccine was investigated in a mouse model in order to see whether it could provide cross-protection against influenza virus infection.

METHODS

The mice were intranasally immunized three times at the 0, 7 and 14 day with vaccine containing 0.2 µg hemagglutinin (HA) and/or without 1,8-cineole. Seven days after the 3rd immunization dose, the mice were infected with 50 µl of 15 LD₅₀ (50% mouse lethal dose) influenza virus A/FM/1/47 (H1N1). On day 6 post-infection, 10 mice per group were sacrificed to collect samples, to take the body weight and lung, and detect the viral load, pathological changes in the lungs and antibody, etc. The collected samples included blood serum and nasal lavage fluids. In addition, the survival experiments were carried out  to investigate the survival of mice.

RESULTS

Mice i.n. inoculated with influenza vaccine and 12.5 mg/kg 1,8-cineole increased the production of influenza-specific serum immunoglobulin (Ig) G2a antibodies, stimulated mucosal secretive IgA (s-IgA) responses at the nasal cavity, improved the expression of respiratory tract intraepithelial lymphocytes (IELs) in the upper respiratory tract, and promoted dendritic cell (DC) maturation and the expression of co-stimulatory molecules cluster of differentiation (CD)40, CD80 and CD86 in peripheral blood. Importantly, mice that had received 1,8-cineole-supplemented influenza vaccine showed longer survival time, milder inflammation, less weight loss and mortality rate and lower lung index and viral titers compared to that of mice immunized a non-1,8-cineole-adjuvanted split vaccine. Thus, i.n. immunization with 1,8-cineole-adjuvanted vaccine induces a superior cross-protective immunity against infection with influenza than an inactivated vaccine only.

CONCLUSION

These results suggest that 1,8-cineole (12.5 mg/kg) has a cross-protection against influenza virus, co-administered with inactivated influenza viral antigen in a mouse model.

Identification of Polo-like kinases as potential novel drug targets for influenza A virus

In recent years genome-wide RNAi screens have revealed hundreds of cellular factors required for influenza virus infections in human cells. The long-term goal is to establish some of them as drug targets for the development of the next generation of antivirals against influenza. We found that several members of the polo-like kinases (PLK), a family of serine/threonine kinases with well-known roles in cell cycle regulation, were identified as hits in four different RNAi screens and we therefore studied their potential as drug target for influenza. We show that knockdown of PLK1, PLK3, and PLK4, as well as inhibition of PLK kinase activity by four different compounds, leads to reduced influenza virus replication, and we map the requirement of PLK activity to early stages of the viral replication cycle. We also tested the impact of the PLK inhibitor BI2536 on influenza virus replication in a human lung tissue culture model and observed strong inhibition of virus replication with no measurable toxicity. This study establishes the PLKs as potential drug targets for influenza and contributes to a more detailed understanding of the intricate interactions between influenza viruses and their host cells.

The MEK-inhibitor CI-1040 displays a broad anti-influenza virus activity in vitro and provides a prolonged treatment window compared to standard of care in vivo

Influenza viruses (IV) continue to pose an imminent threat to human welfare. Yearly re-occurring seasonal epidemic outbreaks and pandemics with high mortality can occur. Besides vaccination against a limited number of viral strains only a few antiviral drugs are available, which are losing their effectiveness as more and more IV strains become resistant. Thus, new antiviral approaches that omit IV resistance are urgently needed. Here, the dependency on the cellular Raf/MEK/ERK signaling pathway for IV replication opens a new perspective. In consequence, we studied the antiviral potential of the MEK inhibitor Cl-1040 (PD184352). We show that Cl-1040 significantly reduces virus titers in vitro via retention of viral RNP complexes in the cell nucleus. Furthermore, Cl-1040 is effective against a broad range of IV strains, including highly pathogenic avian IV, as well as against a Tamiflu^®-resistant IV strain. Using a mouse model, we demonstrate that Cl-1040 can reduce IV lung titers in vivo. Importantly, the treatment window for Cl-1040 expands up to 48 h post infection when Tamiflu^® treatment has no effect. In conclusion, Cl-1040 offers an interesting perspective for anti-IV approaches.

Cell Cycle-independent Role of Cyclin D3 in Host Restriction of Influenza Virus Infection

To identify new host factors that modulate the replication of influenza A virus, we performed a yeast two-hybrid screen using the cytoplasmic tail of matrix protein 2 from the highly pathogenic H5N1 strain. The screen revealed a high-score interaction with cyclin D3, a key regulator of cell cycle early G₁ phase. M2-cyclin D3 interaction was validated through GST pull-down and recapitulated in influenza A/WSN/33-infected cells. Knockdown of Ccnd3 by small interfering RNA significantly enhanced virus progeny titers in cell culture supernatants. Interestingly, the increase in virus production was due to cyclin D3 deficiency per se and not merely a consequence of cell cycle deregulation. A combined knockdown of Ccnd3 and Rb1, which rescued cell cycle progression into S phase, failed to normalize virus production. Infection by influenza A virus triggered redistribution of cyclin D3 from the nucleus to the cytoplasm, followed by its proteasomal degradation. When overexpressed in HEK 293T cells, cyclin D3 impaired binding of M2 with M1, which is essential for proper assembly of progeny virions, lending further support to its role as a putative restriction factor. Our study describes the identification and characterization of cyclin D3 as a novel interactor of influenza A virus M2 protein. We hypothesize that competitive inhibition of M1-M2 interaction by cyclin D3 impairs infectious virion formation and results in attenuated virus production. In addition, we provide mechanistic insights into the dynamic interplay of influenza virus with the host cell cycle machinery during infection.

[Antiviral activities against influenza virus (FM1) of bioactive fractions and representative compounds extracted from Banlangen (Radix Isatidis)]

Objective

To study the antiviral activities of clemastanin B (CB), epigoitrin, phenylpropanoids portion (PEP) and the mixture of phenylpropanoids, alkaloids and organic acid fractions (PEP + ALK + OA) from Banlangen (Radix Isatidis).

Methods

The experiment consisted of four parts: therapeutic action, prophylaxsis action, inhibition of virus attachment, and direct virucidal action. Cytopathic effect (CPE) and 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium (MTT) were used to assess antiviral activity.

Results

CB, epigoitrin, PEP and PEP + ALK + OA fractions from Banlangen (Radix Isatidis) extract significantly increased the viability of MDCK cells pre-infected with the virus compared with the virus control group in all the dilutions (P < 0.01). Pretreated with either pure compounds or chemical fractions of Banlangen (Radix Isatidis) extract in all the dilutions significantly improved the viability of MDCK cells (P < 0.01). The inhibition of virus absorption to the host cells by CB, epigoitrin and PEP was in a dose dependent manner.

Conclusion

CB, epigoitrin, PEP and PEP + ALK + OA exert their anti-influenza activity by inhibiting the virus multiplication, prophylaxsis and blocking the virus attachment. The primary mode of action of PEP and PEP + ALK + OA is the inhibition of virus replication. The inhibitory effects on virus attachment and multiplication are the main modes for epigoitrin.

Antivirals for Respiratory Viral Infections: Problems and Prospects

In the past two decades, several newly emerging and reemerging viral respiratory pathogens including several influenza viruses (avian influenza and pandemic influenza), severe acute respiratory syndrome coronavirus (SARS-CoV), and Middle East respiratory syndrome coronavirus (MERS-CoV), have continued to challenge medical and public health systems. Thereafter, the development of cost-effective, broad-spectrum antiviral agents is the urgent mission of both virologists and pharmacologists. Current antiviral developments have focused targets on viral entry, replication, release, and intercellular pathways essential for viral life cycle. Here, we review the current literature on challenges and prospects in the development of these antivirals.

The Amino Acid Substitution Q65H in the 2C Protein of Swine Vesicular Disease Virus Confers Resistance to Golgi Disrupting Drugs

Swine vesicular disease virus (SVDV) is a porcine pathogen and a member of the species Enterovirus B within the Picornaviridae family. Brefeldin A (BFA) is an inhibitor of guanine nucleotide exchange factors of Arf proteins that induces Golgi complex disassembly and alters the cellular secretory pathway. Since BFA has been shown to inhibit the RNA replication of different enteroviruses, including SVDV, we have analyzed the effect of BFA and of golgicide A (GCA), another Golgi disrupting drug, on SVDV multiplication. BFA and GCA similarly inhibited SVDV production. To investigate the molecular basis of the antiviral effect of BFA, SVDV mutants with increased resistance to BFA were isolated. A single amino acid substitution, Q65H, in the non-structural protein 2C was found to be responsible for increased resistance to BFA. These results provide new insight into the relationship of enteroviruses with the components of the secretory pathway and on the role of SVDV 2C protein in this process.

Influenza A Virus and Influenza B Virus Can Induce Apoptosis via Intrinsic or Extrinsic Pathways and Also via NF-κB in a Time and Dose Dependent Manner

Influenza viruses are able to cause annual epidemics and pandemics due to their mutation rates and reassortment capabilities leading to antigenic shifts and drifts. To identify host response to influenza A and B viruses on A549 and MDCK II cells at low and high MOIs, expressions of MxA and caspases 3, 8, and 9 and BAD, TNFα, and IκBα genes were measured in the cells supernatants. H1N1 and H3N2 prefer to initially enhance the intrinsic pathway, determined by higher caspase 9 activity in MDCK II cells compared to caspase 8 activity and vice versa in A549 cells at different MOIs, while INF B prefers extrinsic pathway in A549 cells according to significant low or undetectable caspase 9 activity and high activity of caspase 8 but also can induce intrinsic pathway in MDCK II cells as determined by significant low or undetectable activity of caspase 8 and high caspase 9 activity at different MOIs; the considerable MxA expression was found in influenza A and B viruses infected A549 and MDCK II cells at low MOIs. In conclusion, influenza A and B viruses induced extrinsic and intrinsic apoptosis in parallel, and the induction was associated with viral infection in a dose dependent manner.

Modes of Antiviral Action of Chemical Portions and Constituents from Woad Root Extract against Influenza Virus A FM1

Woad root has been used for the prevention of influenza for hundreds of years in many Asian countries. In this study, the antiviral modes of clemastanin B (CB), epigoitrin, phenylpropanoid portion (PEP), and the mixture of phenylpropanoids, alkaloids, and organic acid portions (PEP + ALK + OA) from wood root extract against influenza virus A FM1 were investigated. The results revealed that CB, epigoitrin, PEP, and PEP + ALK + OA exert their anti-influenza activity via inhibiting the virus multiplication, prophylaxis, and blocking the virus attachment. The primary mode of action of PEP and PEP + ALK + OA is the inhibition of virus replication. The inhibitory effect on virus attachment and multiplication is the main modes for epigoitrin. All the compounds or chemical portions from woad root extract tested in this study do not have direct virucidal activity. Our results provided the comprehensive analysis of the antiviral mechanism of wood root extract.

Anti-inflammatory effects of indirubin derivatives on influenza A virus-infected human pulmonary microvascular endothelial cells

Influenza A virus (IAV) poses global threats to human health. Acute respiratory distress syndrome and multi-organ dysfunction are major complications in patients with severe influenza infection. This may be explained by the recent studies which highlighted the role of the pulmonary endothelium as the center of innate immune cells recruitment and excessive pro-inflammatory cytokines production. In this report, we examined the potential immunomodulatory effects of two indirubin derivatives, indirubin-3′-(2,3-dihydroxypropyl)-oximether (E804) and indirubin-3′-oxime (E231), on IAV (H9N2) infected-human pulmonary microvascular endothelial cells (HPMECs). Infection of H9N2 on HPMECs induced a high level of chemokines and cytokines production including IP-10, RANTES, IL-6, IFN-β and IFN-γ1. Post-treatment of E804 or E231 could significantly suppress the production of these cytokines. H9N2 infection rapidly triggered the activation of innate immunity through phosphorylation of signaling molecules including mitogen-activated protein kinases (MAPKs) and signal transducer and activator of transcription (STAT) proteins. Using specific inhibitors or small-interfering RNA, we confirmed that indirubin derivatives can suppress H9N2-induced cytokines production through MAPKs and STAT3 signaling pathways. These results underscore the immunomodulatory effects of indirubin derivatives on pulmonary endothelium and its therapeutic potential on IAV-infection.

Antiviral Drugs

Viruses are major pathogenic agents causing a variety of serious diseases in humans, other animals, and plants.

Drugs that combat viral infections are called antiviral drugs. There are no effective antiviral drugs for many viral infections. However, there are several drugs for influenza, a couple of drugs for herpesviruses, and some new antiviral drugs for treatment of HIV and hepatitis C infections.

The arsenal of antivirals is complex. As of March 2014, it consists of approximately 50 drugs approved by the FDA, approximately half of which are directed against HIV. Antiviral drug creation strategies are focused on two different approaches: targeting the viruses themselves or targeting host cell factors.

Direct virus-targeting antiviral drugs include attachment inhibitors, entry inhibitors, uncoating inhibitors, protease inhibitors, polymerase inhibitors, nucleoside and nucleotide reverse transcriptase inhibitors, nonnucleoside reverse-transcriptase inhibitors, and integrase inhibitors.

Protease inhibitors (darunavir, atazanavir, and ritonavir), viral DNA polymerase inhibitors (acyclovir, valacyclovir, valganciclovir, and tenofovir), and an integrase inhibitor (raltegravir) are included in the list of Top 200 Drugs by sales for the 2010s.

Measuring Attachment and Internalization of Influenza A Virus in A549 Cells by Flow Cytometry

Attachment to target cells followed by internalization are the very first steps of the life cycle of influenza A virus (IAV). We provide here a detailed protocol for measuring relative changes in the amount of viral particles that attach to A549 cells, a human lung epithelial cell line, as well as in the amount of particles that are internalized into the cell. We use biotinylated virus which can be easily detected following staining with Cy3-labeled streptavidin (STV-Cy3). We describe the growth, purification and biotinylation of A/WSN/33, a widely used IAV laboratory strain. Cold-bound biotinylated IAV particles on A549 cells are stained with STV-Cy3 and measured using flow cytometry. To investigate uptake of viral particles, cold-bound virus is allowed to internalize at 37 °C. In order to differentiate between external and internalized viral particles, a blocking step is applied: Free binding spots on the biotin of attached virus on the cell surface are bound by unlabeled streptavidin (STV). Subsequent cell permeabilization and staining with STV-Cy3 then enables detection of internalized viral particles. We present a calculation to determine the relative amount of internalized virus. This assay is suitable to measure effects of drug-treatments or other manipulations on attachment or internalization of IAV.

Lariciresinol-4-O-β-D-glucopyranoside from the root of Isatis indigotica inhibits influenza A virus-induced pro-inflammatory response

ETHNOPHARMACOLOGICAL RELEVANCE

Isatis indigotica is a traditional Chinese medicine. Its dried roots named "ban lan gen" in Chinese, are used for clinical treatment of virus infection, tumor, inflammation with a long history. However, its anti-influenza active ingredient and the underlying mechanism remain unclear. In this study, the anti-influenza and anti-inflammatory effects of a lignan glycoside: lariciresinol-4-O-β-D-glucopyranoside isolated from the root of I. indigotica on human alveolar epithelial cell line A549 infected with influenza A virus were investigated.

MATERIALS AND METHODS

Chemical and spectroscopic methods were employed to identify the structure of the lignan glycoside. Cytotoxicity of the lignan glycoside was analyzed using methylthiazolyltetrazolium (MTT) assay. The inhibitory activity against influenza virus of the lignan was determined by CPE inhibition assay. HEK-293 cells stably co-transfected with NF-κB responsive firefly luciferase and constitutively expressing GFP were employed for monitoring the effect of the lignan on NF-κB signal pathway activation. Nuclear export of viral ribonucleoprotein (RNP) complexes was monitored by indirect immunofluorescence. Quantitative real-time PCR was used to quantify the expression profiling of cytokines and chemokines after infection with influenza virus.

RESULTS

We showed that the lignan glycoside treatment was effective against the influenza A virus-induced cytopathic effect (CPE) in MDCK cells. Further study demonstrated the lignan glycoside attenuated virus-induced NF-κB activation, but did not affect export of viral ribonucleoprotein (RNP) complexes from the nucleus in late stages of infection. We revealed that the lignan glycoside suppressed influenza A virus (H1N1)-induced expression of the pro-inflammatory molecules IL-6, TNF-α, IL-8, MCP-1, IP-10 and IFN-α. Moreover, the cytokines and chemokines profiles induced by H9N2 virus resembled those of influenza virus H1N1, but the lignan glycoside reduced the expression of IP-10 and TNF-α.

CONCLUSIONS

Our results suggest that the lignan glycoside is a bioactive component of I. indigotica which may contribute an adjunct to pharmacotherapy for influenza virus infection.

Effect of sesamin against cytokine production from influenza type A H1N1-induced peripheral blood mononuclear cells: computational and experimental studies

In 2009, swine flu (H1N1) had spread significantly to levels that threatened pandemic influenza. There have been many treatments that have arisen for patients since the WHO first reported the disease. Although some progress in controlling influenza has taken place during the last few years, the disease is not yet under control. The development of new and less expensive anti-influenza drugs is still needed. Here, we show that sesamin from the seeds of the Thai medicinal plant Sesamum indicum has anti-inflammatory cytokines in human peripheral blood mononuclear cells (PBMCs) induced by 2009 influenza virus type A H1N1. In this study, the combinatorial screening method combined with the computational approach was applied to investigate the new molecular binding structures of sesamin against the 2009 influenza virus type A H1N1 (p09N1) crystallized structure. Experimental methods were applied to propose the mechanisms of sesamin against cytokine production from H1N1-induced human PBMC model. The molecular dynamics simulation of sesamin binding with the p09N1 crystallized structure showed new molecular binding structures at ARG118, ILE222, ARG224, and TYR406, and it has been proposed that sesamin could potentially be used to produce anti-H1N1 compounds. Furthermore, the mechanisms of sesamin against cytokine production from influenza type A H1N1-induced PBMCs by ELISA and signaling transduction showed that sesamin exhibits the ability to inhibit proinflammatory cytokines, IL-1β and TNF-α, and to enhance the activity of the immune cell cytokine IL-2 via downregulating the phosphorylated JNK, p38, and ERK1/2 MAPK signaling pathways. This information might very well be useful in the prevention and treatment of immune-induced inflammatory disorders.

Pedilanthus tithymaloides Inhibits HSV Infection by Modulating NF-κB Signaling

Pedilanthus tithymaloides (PT), a widely used ethnomedicinal plant, has been employed to treat a number of skin conditions. To extend its utility and to fully exploit its medicinal potential, we have evaluated the in vitro antiviral activity of a methanolic extract of PT leaves and its isolated compounds against Herpes Simplex Virus type 2 (HSV-2). Bioactivity-guided studies revealed that the extract and one of its constituents, luteolin, had potent antiviral activity against wild-type and clinical isolates of HSV-2 (EC₅₀ 48.5–52.6 and 22.4–27.5 μg/ml, respectively), with nearly complete inhibition at 86.5–101.8 and 40.2–49.6 μg/ml, respectively. The inhibitory effect was significant (p<0.001) when the drug was added 2 h prior to infection, and was effective up to 4 h post-infection. As viral replication requires NF-κB activation, we examined whether the observed extract-induced inhibition of HSV-2 was related to NF-κB inhibition. Interestingly, we observed that treatment of HSV-2-infected cells with extract or luteolin suppressed NF-κB activation. Although NF-κB, JNK and MAPK activation was compromised during HSV replication, neither the extract nor luteolin affected HSV-2-induced JNK1/2 and MAPK activation. Moreover, the PT leaf extract and luteolin potently down-regulated the expression of tumor necrosis factor (TNF)-α, Interleukin (IL)-1β, IL-6, NO and iNOS and the production of gamma interferon (IFN-γ), which are directly involved in controlling the NF-κB signaling pathway. Thus, our results indicate that both PT leaf extract and luteolin modulate the NF-κB signaling pathway, resulting in the inhibition of HSV-2 replication.

Cathepsin W Is Required for Escape of Influenza A Virus from Late Endosomes

Human cathepsin W (CtsW) is a cysteine protease, which was identified in a genome-wide RNA interference (RNAi) screen to be required for influenza A virus (IAV) replication. In this study, we show that reducing the levels of expression of CtsW reduces viral titers for different subtypes of IAV, and we map the target step of CtsW requirement to viral entry. Using a set of small interfering RNAs (siRNAs) targeting CtsW, we demonstrate that knockdown of CtsW results in a decrease of IAV nucleoprotein accumulation in the nuclei of infected cells at 3 h postinfection. Assays specific for the individual stages of IAV entry further show that attachment, internalization, and early endosomal trafficking are not affected by CtsW knockdown. However, we detected impaired escape of viral particles from late endosomes in CtsW knockdown cells. Moreover, fusion analysis with a dual-labeled influenza virus revealed a significant reduction in fusion events, with no detectable impact on endosomal pH, suggesting that CtsW is required at the stage of viral fusion. The defect in IAV entry upon CtsW knockdown could be rescued by ectopic expression of wild-type CtsW but not by the expression of a catalytically inactive mutant of CtsW, suggesting that the proteolytic activity of CtsW is required for successful entry of IAV. Our results establish CtsW as an important host factor for entry of IAV into target cells and suggest that CtsW could be a promising target for the development of future antiviral drugs.

IMPORTANCE

Increasing levels of resistance of influenza viruses to available antiviral drugs have been observed. Development of novel treatment options is therefore of high priority. In parallel to the classical approach of targeting viral enzymes, a novel strategy is pursued: cell-dependent factors of the virus are identified with the aim of developing small-molecule inhibitors against a cellular target that the virus relies on. For influenza A virus, several genome-wide RNA interference (RNAi) screens revealed hundreds of potential cellular targets. However, we have only limited knowledge on how these factors support virus replication, which would be required for drug development. We have characterized cathepsin W, one of the candidate factors, and found that cathepsin W is required for escape of influenza virus from the late endosome. Importantly, this required the proteolytic activity of cathepsin W. We therefore suggest that cathepsin W could be a target for future host cell-directed antiviral therapies.

Influenza virus-induced lung injury: pathogenesis and implications for treatment

The influenza viruses are some of the most important human pathogens, causing substantial seasonal and pandemic morbidity and mortality. In humans, infection of the lower respiratory tract of can result in flooding of the alveolar compartment, development of acute respiratory distress syndrome and death from respiratory failure. Influenza-mediated damage of the airway, alveolar epithelium and alveolar endothelium results from a combination of: 1) intrinsic viral pathogenicity, attributable to its tropism for host airway and alveolar epithelial cells; and 2) a robust host innate immune response, which, while contributing to viral clearance, can worsen the severity of lung injury. In this review, we summarise the molecular events at the virus-host interface during influenza virus infection, highlighting some of the important cellular responses. We discuss immune-mediated viral clearance, the mechanisms promoting or perpetuating lung injury, lung regeneration after influenza-induced injury, and recent advances in influenza prevention and therapy.

Prostaglandin A1 inhibits avian influenza virus replication at a postentry level: Effect on virus protein synthesis and NF-κB activity

Influenza A viruses (IAV) have the potential to cause devastating pandemics. In recent years, the emergence of new avian strains able to infect humans represents a serious threat to global human health. The increase in drug-resistant IAV strains underscores the need for novel approaches to anti-influenza chemotherapy. Herein we show that prostaglandin-A1 (PGA1) possesses antiviral activity against avian IAV, including H5N9, H7N1 and H1N1 strains, acting at a level different from the currently available anti-influenza drugs. PGA1 acts at postentry level, causing dysregulation of viral protein synthesis and preventing virus-induced disassembly of host microtubular network and activation of pro-inflammatory factor NF-κB. The antiviral activity is dependent on the presence of a cyclopentenone ring structure and is associated with activation of a cytoprotective heat shock response in infected cells. The results suggest that cyclopentenone prostanoids or prostanoids-derived molecules may represent a new tool to combat avian influenza virus infection.

CYLD negatively regulates nontypeable Haemophilus influenzae-induced IL-8 expression via phosphatase MKP-1-dependent inhibition of ERK

Nontypeable Haemophilus influenzae (NTHi), a Gram-negative bacterium, is the primary cause of otitis media in children and the exacerbation of chronic obstructive pulmonary disease in adults. A hallmark of both diseases is an overactive inflammatory response, including the upregulation of chemokines, such as interleukin-8 (IL-8). An appropriate inflammatory response is essential for eradicating pathogens. However, excessive inflammation can cause host tissue damage. Therefore, expression of IL-8 must be tightly regulated. We previously reported that NTHi induces IL-8 expression in an ERK-dependent manner. We also have shown that the deubiquitinase cylindromatosis (CYLD) suppresses NTHi-induced inflammation. However, the underlying molecular mechanism of how CYLD negatively regulates ERK-mediated IL-8 production is largely unknown. Here, we examine both human lung epithelial A549 cells and lung of Cyld^−/− mice to show that CYLD specifically targets the activation of ERK. Interestingly, CYLD enhances NTHi-induced upregulation of another negative regulator, MAP Kinase Phosphatase-1 (MKP-1), which, in turn, leads to reduced ERK activation and subsequent suppression of IL-8. Taken together, the CYLD suppression of ERK-dependent IL-8 via MKP-1 may bring novel insights into the tight regulation of inflammatory responses and also lead to innovative therapeutic strategies for controlling these responses by targeting key negative regulators of inflammation.