Current and future antiviral therapy of severe seasonal and avian influenza

Antisense oligonucleotides targeting the RNA binding region of the NP gene inhibit replication of highly pathogenic avian influenza virus H5N1

The H5N1 avian influenza virus (AIV) causes widespread infections in bird and human respiratory tracts, and vaccines and drug therapy are limited in their effectiveness. Recent studies of AIV structures have been published and provide new targets for designing antiviral drugs such as antisense oligonucleotides (AS ODNs), which effectively inhibit gene replication. In this study, we designed and synthesized three AS ODNs (NP267, NP628, NP749) that were specific for the RNA binding region of nucleoprotein (NP) based on AIV structure. Results showed that all three AS ODNs could inhibit viral replication in MDCK cells. The NP628 showed the best antiviral effect of all through viral titers, quantitative RT-PCR and indirect immunofluorescence (IFA) assays. In addition, the liposome mediated NP628 could partially protect the mice from a lethal H5N1 influenza virus challenge. Moreover, the NP628 group had a lower viral titer and lung index in the infected mice when compared with the viral control. Our results showed that AS ODN targeting of the AIV NP gene could potently inhibit AIV H5N1 reproduction, thus, formulating a candidate for an emergent therapeutic drug for the pathogenic H5N1 influenza virus infection.

Silymarin efficacy against influenza A virus replication

The anti-influenza A/PR/8/34 virus activity of silymarin was evaluated in MDCK cells and investigated the effect of silymarin on synthesis of viral mRNAs. Silymarin was investigated for its antiviral activity against influenza A/PR virus using a cytopathic effect (CPE) reduction method. Silymarin exhibited anti-influenza A/PR/8/34 virus activity of 98% with no cytotoxicity at the concentration of 100 μg/ml reducing the formation of a visible CPE. Oseltamivir also did show moderate antiviral activity of about 52% against influenza A/PR/8/34 virus at the concentration of 100 μg/ml. Furthermore, the mechanism of anti-influenza virus action in the inhibition of viral mRNA synthesis was analyzed by Reverse Transcriptase-Polymerase Chain Reaction (RT-PCR), and the data indicated an inhibitory effect in late viral RNA synthesis compared with oseltamivir in the presence of 100 μg/ml of silymarin. Therefore, the potential of silymarin for use in treating influenza virus infection merits greater attention.

A highly conserved neutralizing epitope on group 2 influenza A viruses

Current flu vaccines provide only limited coverage against seasonal strains of influenza viruses. The identification of V(H)1-69 antibodies that broadly neutralize almost all influenza A group 1 viruses constituted a breakthrough in the influenza field. Here, we report the isolation and characterization of a human monoclonal antibody CR8020 with broad neutralizing activity against most group 2 viruses, including H3N2 and H7N7, which cause severe human infection. The crystal structure of Fab CR8020 with the 1968 pandemic H3 hemagglutinin (HA) reveals a highly conserved epitope in the HA stalk distinct from the epitope recognized by the V(H)1-69 group 1 antibodies. Thus, a cocktail of two antibodies may be sufficient to neutralize most influenza A subtypes and, hence, enable development of a universal flu vaccine and broad-spectrum antibody therapies.

Findings from a household randomized controlled trial of hand washing and face masks to reduce influenza transmission in Bangkok, Thailand

BACKGROUND

Evidence is needed on the effectiveness of non-pharmaceutical interventions (NPIs) to reduce influenza transmission.

METHODOLOGY

We studied NPIs in households with a febrile, influenza-positive child. Households were randomized to control, hand washing (HW), or hand washing plus paper surgical face masks (HW + FM) arms. Study nurses conducted home visits within 24 hours of enrollment and on days 3, 7, and 21. Respiratory swabs and serum were collected from all household members and tested for influenza by RT-PCR or serology.

PRINCIPAL FINDINGS

Between April 2008 and August 2009, 991 (16·5%) of 5995 pediatric influenza-like illness patients tested influenza positive. Four hundred and forty-two index children with 1147 household members were enrolled, and 221 (50·0%) were aged <6 years. Three hundred and ninety-seven (89·8%) households reported that the index patient slept in the parents' bedroom. The secondary attack rate was 21·5%, and 56/345 (16·3%; 95% CI 12·4-20·2%) secondary cases were asymptomatic. Hand-washing subjects reported 4·7 washing episodes/day, compared to 4·9 times/day in the HW + FM arm and 3·9 times/day in controls (P = 0·001). The odds ratios (ORs) for secondary influenza infection were not significantly different in the HW arm (OR = 1·20; 95% CI 0·76-1·88; P-0.442), or the HW + FM arm (OR = 1·16; 95% CI .0·74-1·82; P = 0.525).

CONCLUSIONS

Influenza transmission was not reduced by interventions to promote hand washing and face mask use. This may be attributable to transmission that occurred before the intervention, poor facemask compliance, little difference in hand-washing frequency between study groups, and shared sleeping arrangements. A prospective study design and a careful analysis of sociocultural factors could improve future NPI studies.

Influenza in immunocompromised patients: considerations for therapy

Influenza infection results in substantial morbidity and mortality in immunocompromised patients, and the risks for influenza and its related complications depend on the degree of immunosuppression. In addition to influenza vaccination and infection control precautions, two classes of antiviral drugs are currently approved for treatment and prophylaxis in uncomplicated infected patients. However, there are no randomized controlled trials assessing the efficacy and safety of licensed antivirals for influenza management in immunocompromised patients. The purpose of this article is to highlight some considerations for therapy in immunocompromised patients, the usefulness of vaccination for the prevention of influenza and the clinical interest in surveillance of antiviral resistance.

Packaging signals in the 5'-ends of influenza virus PA, PB1, and PB2 genes as potential targets to develop nucleic-acid based antiviral molecules

In a previous study a 15-mer phosphorothioate oligonucleotide (S-ON) derived from the packaging signal in the 5' end of segment 1 (PB2) of influenza A virus (designated 5-15b) proved markedly inhibitory to virus replication. Here we investigated whether analogous inhibitory S-ONs targeting the 5' end of segments 2 (PB1) and 3 (PA) could be identified and whether viral resistance to S-ONs can be developed. Similar to our earlier result, 20-mer S-ONs reproducing the 5' ends of segments 2 or 3 (complementary to the 3'-coding regions of PB1 and PA, respectively) exerted a powerful antiviral activity against a variety of influenza A virus subtypes in MDCK cells. Serial passage of the A/Taiwan/1/86 H1N1 strain in the presence of S-ON 5-15b or its antisense as5-15b analogue showed that mutant viruses with reduced susceptibility to the S-ON could indeed be generated, although the resistant viruses displayed reduced replicative fitness. Sequencing the resistant viruses identified mutations in the PB1, PB2, PA and M1 genes. Introduction of these changes into the A/PR/8/34 H1N1 strain by reverse genetics, suggested that alterations to RNA function in the packaging regions of segments 2 and 3 were important in developing resistance to S-ON inhibition. However, many of the other sequence changes induced by S-ON treatment were markedly deleterious to virus fitness. We conclude that packaging signals in the influenza A virus polymerase segments provide feasible targets for nucleic acid-based antivirals that may be difficult for the virus to evade through resistance mutations.

The next ten stories on antiviral drug discovery (part E): advents, advances, and adventures

This review article presents the fifth part (part E) in the series of stories on antiviral drug discovery. The ten stories belonging to this fifth part are dealing with (i) aurintricarboxylic acid; (ii) alkenyldiarylmethanes; (iii) human immunodeficiency virus (HIV) integrase inhibitors; (iv) lens epithelium‐derived growth factor as a potential target for HIV proviral DNA integration; (v) the status presens of neuraminidase inhibitors NAIs in the control of influenza virus infections; (vi) the status presens on respiratory syncytial virus inhibitors; (vii) tricyclic (1,N‐2‐ethenoguanine)‐based acyclovir and ganciclovir derivatives; (viii) glycopeptide antibiotics as antivirals targeted at viral entry; (ix) the potential (off‐label) use of cidofovir in the treatment of polyoma (JC and BK) virus infections; and (x) finally, thymidine phosphorylase as a target for both antiviral and anticancer agents. © 2009 Wiley Periodicals, Inc. Med Res Rev, 31, No. 1, 118–160, 2010

Influenza pharmacotherapy: present situation, strategies and hopes

INTRODUCTION

Influenza is a serious health threat for people of all ages. The causative virus is evolving continuously and the risk of an unexpected mutant, which cannot be controlled by seasonal vaccination, is real. New and more effective antiviral drugs are needed.

AREAS COVERED

This review examines the antiviral drugs with confirmed efficacy in combating influenza, as well as newer compounds that are currently undergoing testing and will hopefully be marketed in the near future. A comprehensive, state-of-the-art picture of drug therapy for influenza is presented, including novel solutions and effective strategies for prescribing currently available antiviral drugs, with emphasis on the importance of updated local epidemiological data, clinical assessment and laboratory testing.

EXPERT OPINION

Current anti-influenza drug research is no longer tied solely to viral envelope protein targets like haemagglutinin and neuraminidase. New drugs act on the viral RNA polymerase complex, which is involved in transcription and replication of the viral genome, and can prevent the maturation, replication and dissemination of numerous viral subtypes. Combating this infection and reducing the duration of symptoms also has important socioeconomic implications related to health-care spending (including hospitalization for complications) and sick-leave pay for workers.

Molecular imaging of influenza and other emerging respiratory viral infections

Research on the pathogenesis and therapy of influenza and other emerging respiratory viral infections would be aided by methods that directly visualize pathophysiologic processes in patients and laboratory animals. At present, imaging of diseases, such as swine-origin H1N1 influenza, is largely restricted to chest radiograph and computed tomography (CT), which can detect pulmonary structural changes in severely ill patients but are more limited in characterizing the early stages of illness, differentiating inflammation from infection or tracking immune responses. In contrast, imaging modalities, such as positron emission tomography, single photon emission CT, magnetic resonance imaging, and bioluminescence imaging, which have become useful tools for investigating the pathogenesis of a range of disease processes, could be used to advance in vivo studies of respiratory viral infections in patients and animals. Molecular techniques might also be used to identify novel biomarkers of disease progression and to evaluate new therapies.

Antioxidant therapy as a potential approach to severe influenza-associated complications

With the appearance of the novel influenza A (H1N1) virus 2009 strain we have experienced a new influenza pandemic and many patients have died from severe complications associated with this pandemic despite receiving intensive care. This suggests that a definitive medical treatment for severe influenza-associated complications has not yet been established. Many studies have shown that superoxide anion produced by macrophages infiltrated into the virus-infected organs is implicated in the development of severe influenza-associated complications. Selected antioxidants, such as pyrrolidine dithiocabamate, N-acetyl-L-cysteine, glutathione, nordihydroguaiaretic acid, thujaplicin, resveratrol, (+)-vitisin A, ambroxol, ascorbic acid, 5,7,4-trihydroxy-8-methoxyflavone, catechins, quercetin 3-rhamnoside, iso- quercetin and oligonol, inhibit the proliferation of influenza virus and scavenge superoxide anion. The combination of antioxidants with antiviral drugs synergistically reduces the lethal effects of influenza virus infections. These results suggest that an agent with antiviral and antioxidant activities could be a drug of choice for the treatment of patients with severe influenza-associated complications. This review article updates knowledge of antioxidant therapy as a potential approach to severe influenza-associated complications.

Novel insights into proteolytic cleavage of influenza virus hemagglutinin

The influenza virus hemagglutinin (HA) mediates the first essential step in the viral life cycle, virus entry into target cells. Influenza virus HA is synthesised as a precursor protein in infected cells and requires cleavage by host cell proteases to transit into an active form. Cleavage is essential for influenza virus infectivity and the HA‐processing proteases are attractive targets for therapeutic intervention. It is well established that cleavage by ubiquitously expressed subtilisin‐like proteases is a hallmark of highly pathogenic avian influenza viruses (HPAIV). In contrast, the nature of the proteases responsible for cleavage of HA of human influenza viruses and low pathogenic avian influenza viruses (LPAIV) is not well understood. Recent studies suggest that cleavage of HA of human influenza viruses might be a cell‐associated event and might be facilitated by the type II transmembrane serine proteases (TTSPs) TMPRSS2, TMPRSS4 and human airway trypsin‐like protease (HAT). Here, we will introduce the different concepts established for proteolytic activation of influenza virus HA, with a particular focus on the role of TTSPs, and we will discuss their implications for viral tropism, pathogenicity and antiviral intervention. Copyright © 2010 John Wiley & Sons, Ltd.

Computer-based de novo designs of tripeptides as novel neuraminidase inhibitors

The latest influenza A (H1N1) pandemic attracted worldwide attention and called for the urgent development of novel antiviral drugs. Here, seven tripeptides are designed and explored as neuraminidase (NA) inhibitors on the structural basis of known inhibitors. Their interactions with NA are studied and compared with each other, using flexible docking and molecular dynamics simulations. The various composed tripeptides have respective binding specificities and their interaction energies with NA decrease in the order of FRI > FRV > FRT > FHV > FRS > FRG > YRV (letters corresponding to amino acid code). The Arg and Phe portions of the tripeptides play important roles during the binding process: Arg has strong electrostatic interactions with the key residues Asp151, Glu119, Glu227 and Glu277, whereas Phe fits well in the hydrophobic cave within the NA active site. Owing to the introduction of hydrophobic property, the interaction energies of FRV and FRI are larger; in particular, FRI demonstrates the best binding quality and shows potential as a lead compound. In addition, the influence of the chemical states of the terminal amino acids are clarified: it is revealed that the charged states of the N-terminus (NH(3) (+)) and C-terminus (COO(-)) are crucial for the tripeptide inhibitory activities and longer peptides may not be appropriate. In addition, the medium inhibiting activity by acetylation of the N-terminus indicates the possible chemical modifications of FRI. Experimental efforts are expected in order to actualize the tripeptides as potent NA inhibitors in the near future.

Oral administration of heat-killed Lactobacillus pentosus strain b240 augments protection against influenza virus infection in mice

Host-defense mechanisms against influenza virus (IFV) infection involve both innate and acquired immunities. Among other components, secretory immunoglobulin A (SIgA) in the airway mucosa plays a particularly pivotal role in preventing IFV infection. Among 150 strains of lactic acid bacteria, Lactobacillus pentosus strain b240 (b240) has the highest IgA-inducing potency in mouse Peyer's patch cells. We previously reported a practical new finding that oral ingestion of nonviable heat-killed b240 elevates salivary IgA secretion in humans. The present study aimed to determine if nonviable b240 can prevent IFV infection in mice. In a BALB/c mouse model infected with lethal levels of IFV A/PR8/34 (H1N1), oral administration of b240 for 3 weeks by gavage prior to IFV infection significantly prolonged the survival period. For IFV infection at nonlethal levels, the infectious titers of IFV in the lungs 7 days after infection were significantly reduced after similar b240 administration. Both anti-IFV IgA and immunoglobulin G titers in bronchoalveolar lavage fluid and plasma on day 7 were significantly higher in the b240-treated group than the control group. The augmentation of the anti-IFV immune response by b240 application was preliminarily confirmed by the elevated production of IFV-driven T-cell factors during mixed lymphocyte reactions with b240-primed splenocytes. These results suggest that oral nonviable heat-killed b240 intake can facilitate protection against IFV infection.

Universal antibodies against the highly conserved influenza fusion peptide cross-neutralize several subtypes of influenza A virus

The fusion peptide of influenza viral hemagglutinin plays a critical role in virus entry by facilitating membrane fusion between the virus and target cells. As the fusion peptide is the only universally conserved epitope in all influenza A and B viruses, it could be an attractive target for vaccine-induced immune responses. We previously reported that antibodies targeting the first 14 amino acids of the N-terminus of the fusion peptide could bind to virtually all influenza virus strains and quantify hemagglutinins in vaccines produced in embryonated eggs. Here we demonstrate that these universal antibodies bind to the viral hemagglutinins in native conformation presented in infected mammalian cell cultures and neutralize multiple subtypes of virus by inhibiting the pH-dependant fusion of viral and cellular membranes. These results suggest that this unique, highly-conserved linear sequence in viral hemagglutinin is exposed sufficiently to be attacked by the antibodies during the course of infection and merits further investigation because of potential importance in the protection against diverse strains of influenza viruses.

Antivirals for influenza: strategies for use in pediatrics

Influenza infection is annually responsible for significant morbidity and mortality, particularly among the very young and old. Recently updated guidelines recommend influenza vaccination of all children aged 6 months to 18 years; however, childhood vaccination remains underutilized. Furthermore, concerns over the reduced efficacy of vaccination in children have further heightened the need for effective treatment schemes. Antiviral therapies have emerged as attractive options in the battle against influenza infection. These agents include the adamantanes (amantadine and rimantadine) and neuraminidase inhibitors (zanamivir, oseltamivir, and peramivir). Broad-scale use of adamantane antivirals has been severely limited in recent years because of high resistance rates and their inability to cover influenza type B. Neuraminidase inhibitors cover influenza types A and B, and have been promulgated to first-line therapy because of historically low resistance rates and relatively infrequent side effects. Moreover, these agents are effective options in combating non-seasonal influenza strains, including H5N1 and pandemic 2009 H1N1. Oseltamivir may be particularly appealing for treating children since it is available in multiple oral dosage formulations, whereas commercially available zanamivir use is limited in young children because it requires inhalation. However, the emergence of resistance to oseltamivir among influenza A strains may limit its usefulness. Additional concerns with neuraminidase inhibitor use in pediatrics center around emerging reports, primarily from Japan, that have temporally linked oseltamivir to significant neuropsychiatric events in children of varying ages. Numerous novel antiviral agents are under development, but most are far from market approval. In addition to treating and preventing the initial burden of pediatric influenza infection, antiviral therapies may significantly reduce secondary bacterial infections (including pneumonia and otitis media), unnecessary antibiotic prescribing, and healthcare-associated costs.

Successful management of fulminant influenza A subtype H1N1 myocarditis

The outbreak and spread of the new influenza A subtype H1N1 reached pandemic levels during 2009, with greater numbers of cases reported daily and numerous complications described. The present report concerns an atypical manifestation of the disease in a previously healthy middle-aged patient who presented with severe, refractory cardiogenic shock 4 days after being diagnosed as having influenza A. The patient was considered for emergency heart transplant. Successful treatment involved the use of a left ventricular assist device, extracorporeal membrane oxygenation, intravenous immunoglobulin and peramivir as therapeutics and bridging therapies for transplant. This case is a report of H1N1 fulminant myocarditis and illustrates the usefulness of a multidisciplinary approach in the care of these patients.

Viral membranes: an emerging antiviral target for enveloped viruses?

Evaluation of: Wolf MC, Freiberg AN, Zhang T et al. A broad-spectrum antiviral targeting entry of enveloped viruses. Proc. Natl Acad. Sci. USA 107, 3157-3162 (2010). The emergence and re-emergence of viruses and the widespread antiviral resistance calls for the development of a broad-spectrum strategy for viral infection. The article under review describes an approach to achieve this goal by developing an antiviral rhodanine derivative effective against enveloped viruses targeting the viral lipid membrane. By intercalating into the viral membrane, the compound irreversibly inactivates the virions with virucidal effects. Potential toxic effects on hosts could be minimized by continuous regeneration of cellular membranes. The present strategy exploits the therapeutic window that exists between static viral membranes and biogenic cellular membranes and provides a useful guideline for future research endeavors towards broad-spectrum antiviral approaches for enveloped viruses. Developing a formulation that ensures efficient delivery and pharmacokinetic properties while minimizing systemic toxicity on cell membranes remains a challenge. The advantages and disadvantages of a viral membrane-targeting approach for the control of emerging and re-emerging viruses will be discussed.

Radiolabeled antiviral drugs and antibodies as virus-specific imaging probes

A number of small-molecule drugs inhibit viral replication by binding directly to virion structural proteins or to the active site of a viral enzyme, or are chemically modified by a viral enzyme before inhibiting a downstream process. Similarly, antibodies used to prevent or treat viral infections attach to epitopes on virions or on viral proteins expressed on the surface of infected cells. Such drugs and antibodies can therefore be thought of as probes for the detection of viral infections, suggesting that they might be used as radiolabeled tracers to visualize sites of viral replication by single-photon emission computed tomography (SPECT) or positron emission tomography (PET) imaging. A current example of this approach is the PET imaging of herpes simplex virus infections, in which the viral thymidine kinase phosphorylates radiolabeled thymidine analogues, trapping them within infected cells. One of many possible future applications might be the use of a radiolabeled hepatitis C protease inhibitor to image infection in animals or humans and provide a quantitative measure of viral burden. This article reviews the basic features of radionuclide imaging and the characteristics of ideal tracer molecules, and discusses how antiviral drugs and antibodies could be evaluated for their suitability as virus-specific imaging probes. The use of labeled drugs as low-dose tracers would provide an alternative application for compounds that have failed to advance to clinical use because of insufficient in vivo potency, an unsuitable pharmacokinetic profile or hepato- or nephrotoxicity.

Dose sparing enabled by skin immunization with influenza virus-like particle vaccine using microneedles

To address the limitations of conventional influenza vaccine manufacturing and delivery, this study investigated administration of virus-like particle (VLP) influenza vaccine using a microneedle patch. The goal was to determine if skin immunization with influenza VLP vaccine using microneedles enables dose sparing. We found that low-dose influenza (A/PR/8/34 H1N1) VLP vaccination using microneedles was more immunogenic than low-dose intramuscular (IM) vaccination and similarly immunogenic as high-dose IM vaccination in a mouse model. With a 1μg dose of vaccine, both routes showed similar immune responses and protective efficacy, with microneedle vaccination being more effective in inducing recall antibody responses in lungs and antibody secreting cells in bone marrow. With a low dose of vaccine (0.3μg), microneedle vaccination induced significantly superior protective immunity, which included binding and functional antibodies as well as complete protection against a high dose lethal infection with A/PR/8/34 virus, whereas IM immunization provided only partial (40%) protection. Therefore, this study demonstrates that microneedle vaccination in the skin confers more effective protective immunity at a lower dose, thus providing vaccine dose-sparing effects.

Antiviral strategies for pandemic and seasonal influenza

While vaccines are the primary public health response to seasonal and pandemic flu, short of a universal vaccine there are inherent limitations to this approach. Antiviral drugs provide valuable alternative options for treatment and prophylaxis of influenza. Here, we will review drugs and drug candidates against influenza with an emphasis on the recent progress of a host-targeting entry-blocker drug candidate, DAS181, a sialidase fusion protein.

Inhibitory effects of carbocisteine on type A seasonal influenza virus infection in human airway epithelial cells

Type A human seasonal influenza (FluA) virus infection causes exacerbations of bronchial asthma and chronic obstructive pulmonary disease (COPD). l-carbocisteine, a mucolytic agent, reduces the frequency of common colds and exacerbations in COPD. However, the inhibitory effects of l-carbocisteine on FluA virus infection are uncertain. We studied the effects of l-carbocisteine on FluA virus infection in airway epithelial cells. Human tracheal epithelial cells were pretreated with l-carbocisteine and infected with FluA virus (H(3)N(2)). Viral titers in supernatant fluids, RNA of FluA virus in the cells, and concentrations of proinflammatory cytokines in supernatant fluids, including IL-6, increased with time after infection. l-carbocisteine reduced viral titers in supernatant fluids, RNA of FluA virus in the cells, the susceptibility to FluA virus infection, and concentrations of cytokines induced by virus infection. The epithelial cells expressed sialic acid with an alpha2,6-linkage (SAalpha2,6Gal), a receptor for human influenza virus on the cells, and l-carbocisteine reduced the expression of SAalpha2,6Gal. l-carbocisteine reduced the number of acidic endosomes from which FluA viral RNA enters into the cytoplasm and reduced the fluorescence intensity from acidic endosomes. Furthermore, l-carbocisteine reduced NF-kappaB proteins including p50 and p65 in the nuclear extracts of the cells. These findings suggest that l-carbocisteine may inhibit FluA virus infection, partly through the reduced expression of the receptor for human influenza virus in the human airway epithelial cells via the inhibition of NF-kappaB and through increasing pH in endosomes. l-carbocisteine may reduce airway inflammation in influenza virus infection.

An antibody against a novel and conserved epitope in the hemagglutinin 1 subunit neutralizes numerous H5N1 influenza viruses

The spread of the recently emerged, highly pathogenic H5N1 avian influenza virus has raised concern. Preclinical studies suggest that passive immunotherapy could be a new form of treatment for H5N1 virus infection. Here, a neutralizing monoclonal antibody (MAb) against the hemagglutinin (HA) of the influenza A/chicken/Hatay/2004 H5N1 virus, MAb 9F4, was generated and characterized. MAb 9F4 binds both the denatured and native forms of HA. It was shown to recognize the HA proteins of three heterologous strains of H5N1 viruses belonging to clades 1, 2.1, and 2.2, respectively. By use of lentiviral pseudotyped particles carrying HA on the surface, MAb 9F4 was shown to effectively neutralize the homologous strain, Hatay04, and another clade 1 strain, VN04, at a neutralization titer of 8 ng/ml. Furthermore, MAb 9F4 also neutralized two clade 2 viruses at a neutralizing titer of 40 ng/ml. The broad cross-neutralizing activity of MAb 9F4 was confirmed by its ability to neutralize live H5N1 viruses of clade 2.2.2. Epitope-mapping analysis revealed that MAb 9F4 binds a previously uncharacterized epitope below the globular head of the HA1 subunit. Consistently, this epitope is well conserved among the different clades of H5N1 viruses. MAb 9F4 does not block the interaction between HA and its receptor but prevents the pH-mediated conformational change of HA. MAb 9F4 was also found to be protective, both prophylactically and therapeutically, against a lethal viral challenge of mice. Taken together, our results showed that MAb 9F4 is a neutralizing MAb that binds a novel and well-conserved epitope in the HA1 subunit of H5N1 viruses.

Influenza pathogenesis: lessons learned from animal studies with H5N1, H1N1 Spanish, and pandemic H1N1 2009 influenza

Because cases of highly pathogenic influenza are rare, no systematic clinical studies have evaluated different therapeutic approaches. Instead, treatment recommendations are aimed at the alleviation of clinical signs and symptoms, especially the restoration of respiratory function, and at the inhibition of virus replication, assuming viral load is responsible for disease phenotype. Studies of highly pathogenic influenza in different animal models, especially nonhuman primates and ferrets, reproduce many of the key observations from clinical cases. Host-response kinetics reveal a delayed but broad activation of genes involved in the innate and acquired immune responses (innate responses produce inflammatory responses), which continue after the virus has been cleared and may contribute importantly to the clinical signs observed. Experimental animal models point to an important role for immune dysregulation in the pathogenesis of highly pathogenic influenza. The use of these models to develop and validate therapeutic approaches is just beginning, but published studies reveal the importance of early treatment with antivirals and show the potential and limitations of approaches aimed at the host response.

H1N1 novel influenza A in pregnant and immunocompromised patients

OBJECTIVE

To describe the increased risk of severe disease and the appropriate management of patients at high risk such as pregnant women and immunosuppressed patients who acquire novel influenza A (H1N1).

DESIGN

Review of the literature regarding influenza A in these patient groups, and review of published and unpublished data with regard to novel influenza A (H1N1).

MAIN RESULTS

Pregnant women are at increased risk for severe pneumonitis and respiratory failure from influenza infection, particularly during pandemics, including the current pandemic. Fetal morbidity is significant, usually resulting from maternal fever and severe hypoxemia. Early antiviral therapy using oseltamivir may be beneficial, and intensive care unit support should target adequate oxygenation at all times. Immunosuppressed patients are at increased risk for influenza, as well as at risk for more severe or prolonged infection. Patients after hematopoietic stem cell transplantation, after lung transplantation, and those receiving chemotherapy for leukemia are at highest risk, whereas the risk for human immunodeficiency virus-infected individuals appears relatively low. Treatment with antiviral therapy may be beneficial, even after the usual cut-off of 48 hrs after symptom onset.

CONCLUSIONS

Optimal management of these patients is preventive by influenza vaccination, but the neuraminidase inhibitor antiviral agents provide effective treatment.

Clarithromycin inhibits type a seasonal influenza virus infection in human airway epithelial cells

Human influenza viruses attach to sialic acid with an alpha2,6linkage (SAalpha2,6Gal) on the airway epithelial cells, and the entry of the viruses into the cells and uncoating of the viruses require low pH of endosomes. Bafilomycin A(1), a macrolide antibiotic and a specific inhibitor of vacuolar H(+)-ATPase, inhibits growth of type A and type B human influenza viruses in Madin-Darby canine kidney cells. However, the inhibitory effects of clinically used macrolide antibiotics on influenza virus infection in human airways have not been studied. To examine the effects of clarithromycin on seasonal human influenza virus infection, cultured human tracheal epithelial cells were infected with type A influenza virus (H3N2). Influenza virus infection increased viral titers and the content of cytokines, including interleukin (IL)-1beta and IL-6, in supernatant fluids, and viral RNA in the cells. Clarithromycin reduced viral titers and the content of cytokines in supernatant fluids, viral RNA in the cells, and the susceptibility to virus infection. Clarithromycin reduced the expression of SAalpha2,6Gal, a receptor for human influenza virus, on the mucosal surface of human tracheae, and the number and fluorescence intensity of acidic endosomes in the cells from which viral ribonucleoproteins enter into the cytoplasm. Furthermore, clarithromycin reduced nuclear factor-kappaB (NF-kappaB) proteins, including p50 and p65, in the nuclear extracts. These results suggest that clarithromycin may inhibit seasonal human influenza virus infection by reducing SAalpha2,6Gal partly through the inhibition of NF-kappaB, and increasing pH in endosomes in airway epithelial cells. Clarithromycin may modulate airway inflammation in influenza virus infection.

Triple combination of amantadine, ribavirin, and oseltamivir is highly active and synergistic against drug resistant influenza virus strains in vitro

The rapid emergence and subsequent spread of the novel 2009 Influenza A/H1N1 virus (2009 H1N1) has prompted the World Health Organization to declare the first pandemic of the 21^st century, highlighting the threat of influenza to public health and healthcare systems. Widespread resistance to both classes of influenza antivirals (adamantanes and neuraminidase inhibitors) occurs in both pandemic and seasonal viruses, rendering these drugs to be of marginal utility in the treatment modality. Worldwide, virtually all 2009 H1N1 and seasonal H3N2 strains are resistant to the adamantanes (rimantadine and amantadine), and the majority of seasonal H1N1 strains are resistant to oseltamivir, the most widely prescribed neuraminidase inhibitor (NAI). To address the need for more effective therapy, we evaluated the in vitro activity of a triple combination antiviral drug (TCAD) regimen composed of drugs with different mechanisms of action against drug-resistant seasonal and 2009 H1N1 influenza viruses. Amantadine, ribavirin, and oseltamivir, alone and in combination, were tested against amantadine- and oseltamivir-resistant influenza A viruses using an in vitro infection model in MDCK cells. Our data show that the triple combination was highly synergistic against drug-resistant viruses, and the synergy of the triple combination was significantly greater than the synergy of any double combination tested (P<0.05), including the combination of two NAIs. Surprisingly, amantadine and oseltamivir contributed to the antiviral activity of the TCAD regimen against amantadine- and oseltamivir-resistant viruses, respectively, at concentrations where they had no activity as single agents, and at concentrations that were clinically achievable. Our data demonstrate that the TCAD regimen composed of amantadine, ribavirin, and oseltamivir is highly synergistic against resistant viruses, including 2009 H1N1. The TCAD regimen overcomes baseline drug resistance to both classes of approved influenza antivirals, and thus may represent a highly active antiviral therapy for seasonal and pandemic influenza.

Trends in global warming and evolution of matrix protein 2 family from influenza A virus

The global warming is an important factor affecting the biological evolution, and the influenza is an important disease that threatens humans with possible epidemics or pandemics. In this study, we attempted to analyze the trends in global warming and evolution of matrix protein 2 family from influenza A virus, because this protein is a target of anti-flu drug, and its mutation would have significant effect on the resistance to anti-flu drugs. The evolution of matrix protein 2 of influenza A virus from 1959 to 2008 was defined using the unpredictable portion of amino-acid pair predictability. Then the trend in this evolution was compared with the trend in the global temperature, the temperature in north and south hemispheres, and the temperature in influenza A virus sampling site, and species carrying influenza A virus. The results showed the similar trends in global warming and in evolution of M2 proteins although we could not correlate them at this stage of study. The study suggested the potential impact of global warming on the evolution of proteins from influenza A virus.

Evidence for a novel gene associated with human influenza A viruses

BACKGROUND

Influenza A virus genomes are comprised of 8 negative strand single-stranded RNA segments and are thought to encode 11 proteins, which are all translated from mRNAs complementary to the genomic strands. Although human, swine and avian influenza A viruses are very similar, cross-species infections are usually limited. However, antigenic differences are considerable and when viruses become established in a different host or if novel viruses are created by re-assortment devastating pandemics may arise.

RESULTS

Examination of influenza A virus genomes from the early 20th Century revealed the association of a 167 codon ORF encoded by the genomic strand of segment 8 with human isolates. Close to the timing of the 1948 pseudopandemic, a mutation occurred that resulted in the extension of this ORF to 216 codons. Since 1948, this ORF has been almost totally maintained in human influenza A viruses suggesting a selectable biological function. The discovery of cytotoxic T cells responding to an epitope encoded by this ORF suggests that it is translated into protein. Evidence of several other non-traditionally translated polypeptides in influenza A virus support the translation of this genomic strand ORF. The gene product is predicted to have a signal sequence and two transmembrane domains.

CONCLUSION

We hypothesize that the genomic strand of segment 8 of encodes a novel influenza A virus protein. The persistence and conservation of this genomic strand ORF for almost a century in human influenza A viruses provides strong evidence that it is translated into a polypeptide that enhances viral fitness in the human host. This has important consequences for the interpretation of experiments that utilize mutations in the NS1 and NEP genes of segment 8 and also for the consideration of events that may alter the spread and/or pathogenesis of swine and avian influenza A viruses in the human population.

Reverse genetics technology for Rift Valley fever virus: current and future applications for the development of therapeutics and vaccines

The advent of reverse genetics technology has revolutionized the study of RNA viruses, making it possible to manipulate their genomes and evaluate the effects of these changes on their biology and pathogenesis. The fundamental insights gleaned from reverse genetics-based studies over the last several years provide a new momentum for the development of designed therapies for the control and prevention of these viral pathogens. This review summarizes the successes and stumbling blocks in the development of reverse genetics technologies for Rift Valley fever virus and their application to the further dissection of its pathogenesis and the design of new therapeutics and safe and effective vaccines.

Genotyping and screening of reassortant live-attenuated influenza B vaccine strain

Live-attenuated influenza virus vaccines can be generated by reassortment of gene segments between an attenuated donor strain and a virulent wild-type virus. The annual production schedule for the seasonal influenza vaccine necessitates rapid and efficient genotyping of the reassorted progeny to identify the desired vaccine strains. This study describes a multiplex RT-PCR system capable of identifying each gene segment from the cold-adapted attenuated donor virus, B/Lee/40ca. The specificity of the amplification system was optimized by testing various wild-type influenza B viruses. The resulting RT-PCR method is sensitive and efficient enough for routine identification of reassortant clones to identify the desired gene constellation, consisting of six segments from the attenuated donor virus and the H and N genes from the wild-type virus. By providing a more rapid and efficient means of genotyping the candidate reassortant strains, this method could be implemented to expedite the generation of each component strain and allow more time to culture and process the final seasonal influenza vaccine.

Development of a multiplex real-time RT-PCR that allows universal detection of influenza A viruses and simultaneous typing of influenza A/H1N1/2009 virus

On June 11, 2009, the World Health Organization declared that the influenza A/H1N1/2009 virus had become the first influenza pandemic of the 21st century. Rapid detection and differentiation from seasonal and avian influenza would be beneficial for patient management and infection control. It was the aim of this study to develop a real-time RT-PCR that can detect all influenza A viruses and offer simultaneous typing for influenza A/H1N1/2009.

This would be a useful addition to existing diagnostic protocols for influenza A. Its routine use would allow laboratories to screen out influenza A/H1N1/2009 positive samples rapidly and would reduce overall testing costs.

Thrombocytopenia from combination treatment with oseltamivir and probenecid: case report, MedWatch data summary, and review of the literature

The possibility of an avian flu pandemic has spurred interest in preventive treatments with antivirals such as oseltamivir. Combining treatment with probenecid to delay excretion may extend limited supplies of oseltamivir. We previously conducted a pharmacokinetic study of oseltamivir plus probenecid among healthy volunteers. In this article, we describe a 68-year-old woman who, during the pharmacokinetic study, developed severe thrombocytopenia 2 weeks after starting oseltamivir plus probenecid. She was receiving no other drug therapy at the time. Her platelet count decreased from 200 to 15 x 10(3)/mm(3), although no clinically evident bleeding abnormalities were noted. The two drugs were discontinued. One week later, without any therapeutic intervention, her platelet count returned to normal. By using the Naranjo adverse drug reaction probability scale to assess the strength of the association between the drugs and the adverse event, a score of 7 was derived for both drugs, indicating that the association was probable. We found no previous literature reports of thrombocytopenia associated with either drug. However, a review of the United States Food and Drug Administration's Adverse Event Reporting System database found 93 cases of thrombocytopenia and/or decreased platelet counts associated with oseltamivir and 24 cases associated with probenecid administration. Signal detection analyses were significant for oseltamivir (p=0.001), but not probenecid. The underlying mechanism of thrombocytopenia with these drugs is unknown. Clinicians should be aware that the use of oseltamivir and probenecid has been reported to be associated with thrombocytopenia.

A(H5N1) Virus Evolution in South East Asia

Highly Pathogenic Avian Influenza (HPAI) H5N1 virus is an ongoing public health and socio-economic challenge, particularly in South East Asia. H5N1 is now endemic in poultry in many countries, and represents a major pandemic threat. Here, we describe the evolution of H5N1 virus in South East Asia, the reassortment events leading to high genetic diversity in the region, and factors responsible for virus spread. The virus has evolved with genetic variations affecting virulence, drug-resistance, and adaptation to new host species. The constant surveillance of these changes is of primary importance in the global efforts of the scientific community.

A proline-based neuraminidase inhibitor: DFT studies on the zwitterion conformation, stability and formation

The designs of potent neuraminidase (NA) inhibitors are an efficient way to deal with the recent "2009 H1N1" influenza epidemic. In this work, density functional calculations were employed to study the conformation, stability and formation of the zwitterions of 5-[(1R,2S)-1-(acetylamino)-2-methoxy-2-methylpentyl]-4-[(1Z)-1-propenyl]-(4S,5R)-d-proline (BL), a proline-based NA inhibitor. Compared to proline, the zwitterion stability of BL is enhanced by 1.76 kcal mol(-1) due to the introduction of functional groups. However, the zwitterion of BL will not represent a local minimum on the potential energy surface until the number of water molecules increases up to two (n = 2). With the addition of two and three water molecules, the energy differences between the zwitterions and corresponding canonical isomers were calculated at 3.13 and -1.54 kcal mol(-1), respectively. The zwitterions of BL are mainly stabilized by the H-bonds with the water molecules, especially in the case of three water molecules where the carboxyl-O atoms are largely coordination-saturated by three H-bonds of medium strengths, causing the zwitterion stability even superior to the canonical isomer. With the presence of two and three water molecules, the energy barriers for the conversion processes from the canonical isomers to the zwitterions are equal to 4.96 and 3.13 kcal mol(-1), respectively. It indicated that the zwitterion formation is facile to take place with addition of two molecules and further facilitated by more water molecules. Besides, the zwitterion formation of BL is finished in a single step, different from other NA inhibitors. Owing to the above advantages, BL is a good NA inhibitor candidate and more attention should be paid to explorations of BL-based drugs.