A pan-influenza antibody inhibiting neuraminidase via receptor mimicry.

Rapidly evolving influenza A viruses (IAVs) and influenza B viruses (IBVs) are major causes of recurrent lower respiratory tract infections. Current influenza vaccines elicit antibodies predominantly to the highly variable head region of haemagglutinin and their effectiveness is limited by viral drift1 and suboptimal immune responses2. Here we describe a neuraminidase-targeting monoclonal antibody, FNI9, that potently inhibits the enzymatic activity of all group 1 and group 2 IAVs, as well as Victoria/2/87-like, Yamagata/16/88-like and ancestral IBVs. FNI9 broadly neutralizes seasonal IAVs and IBVs, including the immune-evading H3N2 strains bearing an N-glycan at position 245, and shows synergistic activity when combined with anti-haemagglutinin stem-directed antibodies. Structural analysis reveals that D107 in the FNI9 heavy chain complementarity-determinant region 3 mimics the interaction of the sialic acid carboxyl group with the three highly conserved arginine residues (R118, R292 and R371) of the neuraminidase catalytic site. FNI9 demonstrates potent prophylactic activity against lethal IAV and IBV infections in mice. The unprecedented breadth and potency of the FNI9 monoclonal antibody supports its development for the prevention of influenza illness by seasonal and pandemic viruses.

Effect of aloin on viral neuraminidase and hemagglutinin-specific T cell immunity in acute influenza.

BACKGROUND: Millions of people are infected by the influenza virus worldwide every year. Current selections of anti-influenza agents are limited and their effectiveness and drug resistance are still of concern. PURPOSE: Investigation on in vitro and in vivo effect of aloin from Aloe vera leaves against influenza virus infection. METHODS: In vitro antiviral property of aloin was measured by plaque reduction assay in which MDCK cells were infected with oseltamivir-sensitive A(H1N1)pdm09, oseltamivir-resistant A(H1N1)pdm09, H1N1 or H3N2 influenza A or with influenza B viruses in the presence of aloin. In vivo activity was tested in H1N1 influenza virus infected mice. Aloin-mediated inhibition of influenza neuraminidase activity was tested by MUNANA assay. Aloin treatment-mediated modulation of anti-influenza immunity was tested by the study of hemagglutinin-specific T cells in vivo. RESULTS: Aloin significantly reduced in vitro infection by all the tested strains of influenza viruses, including oseltamivir-resistant A(H1N1)pdm09 influenza viruses, with an average IC50 value 91.83 ± 18.97 µM. In H1N1 influenza virus infected mice, aloin treatment (intraperitoneal, once daily for 5 days) reduced virus load in the lungs and attenuated body weight loss and mortality. Adjuvant aloin treatment also improved the outcome with delayed oseltamivir treatment. Aloin inhibited viral neuraminidase and impeded neuraminidase-mediated TGF-ß activation. Viral neuraminidase mediated immune suppression with TGF-ß was constrained and influenza hemagglutinin-specific T cell immunity was increased. There was more infiltration of hemagglutinin-specific CD4+ and CD8+ T cells in the lungs and their production of effector cytokines IFN-γ and TNF-α was boosted. CONCLUSION: Aloin from Aloe vera leaves is a potent anti-influenza compound that inhibits viral neuraminidase activity, even of the oseltamivir-resistant influenza virus. With suppression of this virus machinery, aloin boosts host immunity with augmented hemagglutinin-specific T cell response to the infection. In addition, in the context of compromised benefit with delayed oseltamivir treatment, adjuvant aloin treatment ameliorates the disease and improves survival. Taken together, aloin has the potential to be further evaluated for clinical applications in human influenza.

Anti-influenza activities of polyphenols from the medicinal mushroom Phellinus baumii.

Five polyphenols were isolated from the ethanolic extract of the fruiting bodies of Phellinus baumii. These compounds were identified by various spectroscopic methods as hispidin, hypholomine B, inoscavin A, davallialactone, and phelligridin D. All compounds inhibited noncompetitively H1N1, H5N1, and H3N2 neuraminidase activity and reduced the amount of virally-induced cytopathic effect (CPE) according to an MDCK cell-based assay.

Antiviral activity of baicalin against influenza A (H1N1/H3N2) virus in cell culture and in mice and its inhibition of neuraminidase.

Scutellaria baicalensis Georgi, a Chinese herbal decoction, has been used for the treatment of the common cold, fever and influenza virus infections. In previous studies, we found that oral administration of baicalein resulted in the inhibition of influenza A virus replication in vivo, which was linked to baicalin in serum. However, the effective dose and underlying mechanisms of the efficacy of baicalin against influenza A virus have not been fully elucidated. In this study, the antiviral effects of baicalin in influenza-virus-infected MDCK cells and mice were examined. The neuraminidase inhibition assay was performed to investigate the mechanism of action of baicalin. In vitro results showed that baicalin exhibited a half-maximal effective concentration (EC50) of 43.3 µg/ml against the influenza A/FM1/1/47 (H1N1) virus and 104.9 µg/ml against the influenza A/Beijing/32/92 (H3N2) virus. When added to MDCK cell cultures after inoculation with influenza virus, baicalin demonstrated obvious antiviral activity that increased in a dose-dependent manner, indicating that baicalin affected virus budding. Baicalin had clear inhibitory effects against neuraminidases, with half-maximal inhibitory concentration (IC50) of 52.3 µg/ml against the influenza A/FM1/1/47 (H1N1) virus and 85.8 µg/ml against the influenza A/Beijing/32/92 (H3N2) virus. In vivo studies showed that an intravenous injection of baicalin effectively reduced the death rate, prolonged the mean day to death (MDD) and improved the lung parameters of mice infected with influenza A virus. These results demonstrate that baicalin acts as a neuraminidase inhibitor, with clear inhibitory activities that are effective against different strains of influenza A virus in both cell culture and a mouse model, and that baicalin has potential utility in the management of influenza virus infections.

Homoisoflavonoids from Caesalpinia sappan displaying viral neuraminidases inhibition.

In this study, twelve neuraminidase (NA) inhibitory compounds 1-12 were isolated from heartwood of Caesalpinia sappan on the basis of their biological activities against three types of viral NAs. Of isolated homoisoflavonoids, sappanone A (2) showed the most potent NAs inhibitory activities with IC(50) values of 0.7 µM [H1N1], 1.1 µM [H3N2], and 1.0 µM [H9N2], respectively, whereas saturated homoisoflavonoid (3) did not show significantly inhibition. This result revealed that α,ß-unsaturated carbonyl group in A-ring was the key requirements for viral NAs inhibitory activity. In our enzyme kinetic study, all NA inhibitors screened were found to be reversible noncompetitive types.

High molecular weight constituents of cranberry interfere with influenza virus neuraminidase activity in vitro.

Cranberry juice contains high molecular weight non-dialyzable material (NDM) which was found to inhibit hemagglutination induced by the influenza virus (IV) as well as to neutralize the cytotoxicity of IV in cell cultures. Because influenza virus surface glycoproteins hemagglutinin (HA) and neuraminidase (NA) are involved in viral replication and in the infectious process, we sought in the present study to examine the effect of NDM on neuraminidases which are the target of most anti-influenza drugs today. NDM inhibited the NA enzymatic activity of influenza A and B strains as well as that of Streptococcus pneumoniae. This finding is of importance considering the emergence of influenza isolates resistant to antiviral drugs, reaching 90 % in some places. The anti-NA activity of NDM, evaluated by the MUNANA method and expressed as the concentration required for 50 % inhibition (IC50), was most potent against N1 (IC50, 192 µg/mL), less active against BN and N2 (IC50, 509 µg/mL and 1128 µg/mL, respectively), and moderately active against Streptococcus pneumoniae NA (IC50, 594 µg/mL). The in vitro findings of the present study suggest that cranberry constituents may have a therapeutic potential against both A and B influenza virus infections and might also interfere with the development of secondary bacterial complications.

[Evaluation of Chinese traditional patent medicines against influenza virus in vitro].

To study in vitro anti-influenza viral activities of Chinese traditional patent medicines for influenza prevention and treatment, neuraminidase (NA) activity assay was used to examine NA inhibitory activity of 33 Chinese traditional patent medicines through fluorimetric assay, and influenza virus induced cytopathic effect (CPE) inhibition assay was used to verify their anti-influenza viral activities in vitro. The assay results showed that most liquid preparations displayed relatively high NA inhibitory activities, such as Shuanghuanglian oral liquid, Qingkailing oral liquid, Qingre Jiedu oral liquid, and Reduning injection. Among liquid preparations, Shuanghuanglian oral liquid not only displayed the highest NA inhibitory effect, but also exhibited obvious in vitro anti-viral activity in CPE experiment. Among solid preparations, Shuanghuanglian powder for injection showed the highest activity on NA inhibition, and Fufang Yuxingcao tablet showed relatively strong anti-influenza viral activity in CPE cells. From the results, it can be concluded that most Chinese traditional patent medicines possessed NA inhibitory activity, but only a few of them displayed significant in vitro anti-influenza viral activities. These results will provide important information for the isolation of active constituents, and for the clinical uses of Chinese traditional patent medicines for influenza treatment and prevention.

Anti-influenza virus activities of flavonoids from the medicinal plant Elsholtzia rugulosa.

ELSHOLTZIA RUGULOSA (Lamiaceae), a common Chinese herb, is widely used in the treatment of cold and fever. In order to elucidate the action mechanism and the active principles from the plant against anti-influenza virus, the influenza virus neuraminidase (NA) activity assay and IN VITRO antiviral activity assay were established, and the isolation of the active principles was guided by NA activity. Finally, 5 active constituents were obtained, namely apigenin ( 1), luteolin ( 2), apiin ( 3), galuteolin ( 4) and luteolin 3'-glucuronyl acid methyl ester ( 5), respectively. They all belong to the flavonoids. The IN VITRO antiviral assay using a cytopathic effect (CPE) reduction method showed that they all possessed anti-influenza virus activity. Among them, apigenin and luteolin exhibited the highest activities against influenza virus (H3N2) with IC (50) values of 1.43 microg/mL and 2.06 microg/mL, respectively. The structure-activity relationship (SAR) of these flavonoids with different chemical structures and their anti-influenza virus activities was addressed in this study.