Neuraminidase Inhibitory Activity Research Articles

An electrochemical impedance sensor for monitoring of gallic acid inhibited neuraminidase activity of PPR HN protein

Peste des petits ruminants (PPR) virus has a surface glycoprotein, hemagglutinin neuraminidase (HN) with functional sites for cell attachment and neuraminidase (NA) activity. The neuraminidase activity of PPR virus (Sungri/96) was biochemically characterized with fluorometric assay, enzyme linked lectin assay (ELLA) and electrochemical impedance spectroscopy (EIS). Furthermore, the inhibitory effect of gallic acid on the virus neuraminidase activity was also evaluated in-vitro in B95a cells. Screen printed carbon electrode were used for the EIS assay. The activity of the viral neuraminidase was presented as the change in charge transfer resistance (Rct). The measurement of neuraminidase activity with EIS was found comparable to ELLA. Cell toxicity (CC50) concentration of gallic acid was found to be 61.0 ± 1.0 µM in B95a cells. A dose dependent effect of gallic acid on the virus neuraminidase activity was observed in both EIS and ELLA measurement. The anti PPRV activity of gallic acid was quantified by cell ELISA and 7.0 ± 1.0 µM was calculated concentration that has 50% viral inhibition in B95a cells. The gallic acid used in present study had neuraminidase inhibitory activity both in ELLA and EIS, furthermore it also reduces the virus propagation in vitro in B95a cells. For high throughput screening of anti-neuraminidase compounds including phytocompounds, electrochemical impedance spectroscopy could be vividly used.

Low response in eliciting neuraminidase inhibition activity of sera among recipients of a split, monovalent pandemic influenza vaccine during the 2009 pandemic.

Antibodies against influenza virus neuraminidase (NA) protein prevent releasing of the virus from host cells and spreading of infection foci and are considered the ‘second line of defence’ against influenza. Haemagglutinin inhibition antibody-low responders (HI-LRs) are present among influenza split vaccine recipients. The NA inhibition (NAI) antibody response in vaccinees is worth exploring, especially those in the HI-LRs population. We collected pre- and post-vaccination sera from 61 recipients of an inactivated, monovalent, split vaccine against A/H1N1pdm09 and acute and convalescent sera from 49 unvaccinated patients naturally infected with the A/H1N1pdm09 virus during the 2009 influenza pandemic. All samples were subjected to haemagglutinin inhibition (HI), NAI and neutralisation assays. Most paired sera from naturally infected patients exhibited marked elevation in the NAI activity, and seroconversion rates (SCR) among HI-LRs and HI-responders (HI-Rs) were 60% and 87%, respectively; however, those from vaccinees displayed low increase in the NAI activity, and the SCR among HI-LRs and HI-Rs were 0% and 12%, respectively. In both HI-LRs and HI-Rs, vaccination with the inactivated, monovalent, split vaccine failed to elicit the NAI activity efficiently in the sera of the naive population, compared with the natural infection. Hence, the improvement of influenza vaccines is warranted to elicit not only HI but also NAI antibodies.

Thiosialoside-decorated polymers use a two-step mechanism to inhibit both early and late stages of influenza virus infection

We describe the preparation of thiosialoside-modified poly (methyl vinyl ether-alt-maleic anhydride) as second-generation polymeric conjugates for the inhibition of influenza virus infection. These synthetic glycopolymers show significantly enhanced neuraminidase inhibitory and antiviral activity in enzyme and cellular levels, respectively. The polyvalent thiosialosides also exhibit comparable inhibitory activity to the first-line anti-influenza drugs Zanamivir® and Oseltamivir® against the PR8 influenza virus strain in virus growth inhibition assays, which may be attributed to multivalent binding to neuraminidase on the virion particles, leading to the virion aggregation and further inhibiting the attaching/fusion and releasing steps in the influenza virus life-cycle. These findings suggest that attaching monomeric sialoside with neuraminidase inhibitory activity to a polymeric scaffold will synergistically disturb both the early and late stages of influenza virus infection, and provides a basis for the development of efficacious anti-viral agents against both wild-type and drug-resistant mutant strains.

Ustusaustin A: a new neuraminidase inhibitory meroterpene from the ascidian-derived endophytic fungus Aspergillus ustus TK-5

A new austin-type meroterpene, namely, ustusaustin A (1), together with seven related known analogues (2–8), were isolated and identified from the culture extract of Aspergillus ustus TK-5, an endophytic fungus obtained from the marine ascidian Pyura momus. The structures of these compounds were established on the basis of detailed interpretation of their NMR and MS data, and the relative and absolute configurations of 1 was confirmed by X-ray crystallographic analysis. Among them, ustusaustin A (1) represents the first example of 1’-nor-austin analogues with an unique 7-benzoylation. Compounds 1–4, 6, and 7 exhibited potent neuraminidase inhibitory activity and this is the first report of neuraminidase inhibitory activity for austin-type meroterpenes.

A Physical Model Overlay of Wild Type Influenza Virus A Neuraminidase and the His274Tyr Mutant Reveals the Basis of Drug Resistance and Catalysis

The influenza virus is the causative agent of the flu, a contagious respiratory illness that causes morbidity, loss of productivity, and, in some instances, death. Although the seasonal flu is typically only life threatening to high‐risk groups, exceptionally virulent forms of the virus that emerge during pandemics, can even threaten strong and otherwise healthy individuals. A strong arsenal of antiviral drugs is essential during a pandemic, but drug resistance threatens our preparedness. A key target for antivirals is neuraminidase, an enzyme that cleaves glycosidic bonds between sialic acid residues on cell surface glycoproteins so that the virus can infect or escape from host cells to repeat the cycle of infection. The enzyme exists as a homo‐tetramer with calcium ions stabilizing the protein structure. Antiviral medications, including Oseltamivir and Zanamivir, inhibit neuraminidase activity but resistance to Oseltamivir is most prevalent. The challenges posed by the rapid evolution of drug resistance have led Dr. Schiffer and her colleagues to develop more innovative ways, based on structural analyses to formulate drugs that are immune to resistance. We chose to focus on resistance of the His274Tyr neuraminidase mutant to the drug Oseltamivir using the crystal structure solved by Collins and colleagues that demonstrates that this resistance is due to a shift in the position of Glu276 into the hydrophobic pocket of the active site. Using the software application, Jmol, we designed physical models based on the overlaid crystal structures of the wild type and the His274Tyr mutant to visualize the shift in Glu276 and its impact on binding of each of three potential ligands: Oseltamivir, Zanamivir, and Sialic Acid. In addition, the catalytic residues Tyr406 and Glu277 were displayed to visualize the lack of impact on catalytic cleavage of the natural substrate, but continued inhibition by Zanamivir. By designing a physical model of Neuraminidase to emphasize the dimensional and catalytic residues, a better understanding of the protein’s function and potential inhibition by drugs can be obtained and may lead to a more effective way to design drugs in the future.Support or Funding InformationSupport for the CREST Project is through NSF‐IUSE #1725940.

Anti-influenza virus phytochemicals from Radix Paeoniae Alba and characterization of their neuraminidase inhibitory activities

Ethnopharmacological relevanceBai Shao (Radix Paeoniae Alba, BS), the root of Paeonia lactiflora Pall., in ancient China was used for Wen Bing (Warm Disease) treatment. Wen Bing has the symptoms of influenza. Ethanol extract of the root has recently been shown to possess anti-influenza activity. However, the active compounds have not yet been identified. AimWe showed that BS aqueous extract was potent in inhibiting influenza A virus in infected cells. We aimed to isolate the bioactive compounds and characterize the anti-influenza mechanism. Materials and methodsPlaque reduction assay was performed for fractions isolated from BS. Hemagglutination inhibition assay and neuraminidase inhibition assay were performed to find the target protein. Molecular docking and reverse genetics were used to confirm the action site of gallic acid on the neuraminidase protein. ResultsWe identified three tannin compounds gallic acid (GA), methyl gallate (MG) and pentagalloylglucose (PGG) in BS aqueous extract that could inhibit the replication of influenza A virus in MDCK cells. While only PGG was found to inhibit the influenza virus-induced hemagglutination of chicken erythrocytes, all three compounds significantly reduced the activity of the neuraminidase. The results from molecular docking and reverse genetics showed that GA interacted with Arg152 of neuraminidase protein. ConclusionThree compounds GA, MG and PGG isolated from BS were found to inhibit influenza A virus in MDCK cells. GA interacts with amino acid Arg152 of the viral neuraminidase. Our study identified anti-influenza compounds of BS and demonstrated their antiviral mechanism, thus providing scientific evidence for using this herb for clinical treatment.

Synthesis, Crystal Structure and Neuraminidase Inhibitory Activity of 1,2,4-Triazole-3-sulfide Derivatives

Synthesis, Crystal Structure and Neuraminidase Inhibitory Activity of 1,2,4-Triazole-3-sulfide Derivatives

Discovery and characterization of a novel peptide inhibitor against influenza neuraminidase

Neuraminidase, an abundant glycoprotein on the influenza virus surface, plays crucial roles in virus replication. Targeting neuraminidase could be a splendid way for the prevention of the spread of influenza infections. Herein, we have identified an octapeptide (errKPAQP) from a synthesized peptide library, originating from mimicking the binding pocket of oseltamivir in neuraminidase, as a potent peptide neuraminidase inhibitor. The docking-based virtual studies showed that errKPAQP exhibited a strong binding affinity (a docking score of -20.03) and nanomolar affinity (11 nM) to influenza neuraminidase, and can inhibit neuraminidase activity at a concentration as low as 4.25 μM, leading to effective protection of MDCK cells from influenza virus-induced death and replication. Furthermore, errKPAQP presented low hemolytic activity, minimal cytotoxicity, and good pharmacokinetic characteristics, which are imperative for an anti-influenza drug. Importantly, errKPAQP was capable of reducing influenza virus-induced inflammation, the serious damage to the lung tissues, and mortality rates in infected mice, indicating that it could protect against the lethal challenge of influenza viruses in vivo. Therefore, we have developed a novel neuraminidase peptide inhibitor with advantageous biological properties and high inhibitory activity towards neuraminidase, and it can serve as a promising anti-influenza drug.

Isocorilagin, isolated from Canarium album (Lour.) Raeusch, as a potent neuraminidase inhibitor against influenza A virus

Canarium album (Lour.) Raeusch (C. album) as a normally medicinal and edible plant has been used widely in Asian countries and is considered a source of phytochemicals that are beneficial to human health. Here, we showed at the first time isocorilagin, a polyphenolic compound isolated from C. album, displayed antiviral activity against diverse strains of influenza A virus (IAV), including A/Puerto Rico/8/34 (H1N1), A/Aichi/2/68 (H3N2) and NA-H274Y (H1N1) with IC50 value of 9.19 ± 1.99, 23.72 ± 2.51 and 4.64 ± 3.01 μM, respectively. Further mechanistic studies revealed that it clearly inhibited neuraminidase activity of IAV and directly influenced the virus release. The molecular docking studies presented isocorilagin could bind to the highly conserved residues in the active sites of NA, implying that isocorilagin may be effective against various influenza strains and not susceptible to produce drug resistance. Taken together, the results strongly suggest that isocorilagin has potential to be an effective, safe and affordable neuraminidase inhibitor against a diverse panel of IAV strains. More importantly, our work expands the biological activities of C. album extracts and provide a new option for the development of anti-influenza drug.

Antiviral Activity of Benzoic Acid Derivative NC-5 Against Influenza A Virus and Its Neuraminidase Inhibition.

The currently available drugs against influenza A virus primarily target neuraminidase (NA) or the matrix protein 2 (M2) ion channel. The emergence of drug-resistant viruses requires the development of new antiviral chemicals. Our study applied a cell-based approach to evaluate the antiviral activity of a series of newly synthesized benzoic acid derivatives, and 4-(2,2-Bis(hydroxymethyl)-5-oxopyrrolidin-l-yl)-3-(5-cyclohexyl-4H-1,2,4-triazol-3-yl)amino). benzoic acid, termed NC-5, was found to possess antiviral activity. NC-5 inhibited influenza A viruses A/FM/1/47 (H1N1), A/Beijing/32/92 (H3N2) and oseltamivir-resistant mutant A/FM/1/47-H275Y (H1N1-H275Y) in a dose-dependent manner. The 50% effective concentrations (EC50) for H1N1 and H1N1-H275Y were 33.6 μM and 32.8 μM, respectively, which showed that NC-5 had a great advantage over oseltamivir in drug-resistant virus infections. The 50% cytotoxic concentration (CC50) of NC-5 was greater than 640 μM. Orally administered NC-5 protected mice infected with H1N1 and H1N1-H275Y, conferring 80% and 60% survival at 100 mg/kg/d, reducing body weight loss, and alleviating virus-induced lung injury. NC-5 could suppress NP and M1 protein expression levels during the late stages of viral biosynthesis and inhibit NA activity, which may influence virus release. Our study proved that NC-5 has potent anti-influenza activity in vivo and in vitro, meaning that it could be regarded as a promising drug candidate to treat infection with influenza viruses, including oseltamivir-resistant viruses.

Bioassay of ferulic acid derivatives as influenza neuraminidase inhibitors.

Four series of ferulic acid derivatives were designed, synthesized, and evaluated for their neuraminidase (NA) inhibitory activities against influenza virus H1N1 in vitro. The pharmacological results showed that the majority of the target compounds exhibited moderate influenza NA inhibitory activity, which was also better than that of ferulic acid. The two most potent compounds were 1m and 4a with IC50 values of 12.77 ± 0.47 and 12.96 ± 1.34 μg/ml, respectively. On the basis of the biological results, a preliminary structure-activity relationship (SAR) was derived and discussed. Besides, molecular docking was performed to study the possible interactions of compounds 1p, 2d, 3b, and 4a with the active site of NA. It was found that the 4-OH-3-OMe group and the amide group (CON) of ferulic acid amide derivatives were two key pharmacophores for NA inhibitory activity. It is meaningful to further modify the natural product ferulic acid to improve its influenza NA inhibitory activity.

Broadly protective human antibodies that target the active site of influenza virus neuraminidase.

Better vaccines against influenza virus are urgently needed to provide broader protection against diverse strains, subtypes, and types. Such efforts are assisted by the identification of novel broadly neutralizing epitopes targeted by protective antibodies. Influenza vaccine development has largely focused on the hemagglutinin, but the other major surface antigen, the neuraminidase, has reemerged as a potential target for universal vaccines. We describe three human monoclonal antibodies isolated from an H3N2-infected donor that bind with exceptional breadth to multiple different influenza A and B virus neuraminidases. These antibodies neutralize the virus, mediate effector functions, are broadly protective in vivo, and inhibit neuraminidase activity by directly binding to the active site. Structural and functional characterization of these antibodies will inform the development of neuraminidase-based universal vaccines against influenza virus.

Chemical constituents from Artemisia rupestris and their neuraminidase inhibitory activity

Two new thiophene derivatives (1 and 2), a new sesquiterpene (3), and 15 known compounds (4–18) were isolated from the whole plants of Artemisia rupestris. The new compounds (1–3) were elucidated by extensive spectroscopic techniques including 1 D (1H and 13C) and 2 D NMR experiments (COSY, HSQC, HMBC and NOESY), and HR-ESI-MS. Most of the isolates (1–6, 8, 10–18) exhibited the neuraminidase inhibitory activity with IC50 values ranging from 74.07–986.54 μM by a fluorescence-based assay. Two known flavonoids (chrysosplenetin B and luteolin) showed a comparable activity to oseltamivir acid on neuraminidase inhibition.

Neuraminidase expressing virus-like particle vaccine provides effective cross protection against influenza virus

Neuraminidase is the second major surface antigen on influenza virus. We investigated the immunogenicity and cross protective efficacy of virus-like particle containing neuraminidase derived from 2009 pandemic H1N1 influenza virus (N1 VLP) in comparison with inactivated split influenza vaccine. Immunization of mice with N1 VLP induced antibody responses specific for virus and cross-reactive neuraminidase inhibition activity whereas an inactivated split vaccine induced strain-specific hemagglutination inhibition activity. N1 VLP-immunized mice developed cross protective immunity against antigenically different influenza viruses, as determined by body weight changes, lung viral titers, infiltrating innate immune cells, and cytokines, and antibody secreting cells, and germinal center B cells. Also, N1 VLP-immune sera provided cross-protection in naïve mice. Immunity by N1 VLP vaccination was not compromised in Fc receptor γ-chain deficient mice. These results suggest that neuraminidase-presenting VLP can be developed as an effective cross-protective vaccine candidate along with current influenza vaccination.

An improved 2D-HPLC-UF-ESI-TOF/MS approach for enrichment and comprehensive characterization of minor neuraminidase inhibitors from Flos Lonicerae Japonicae

Flos Lonicerae Japonicae(Jinyinhua) possesses clearing heat and detoxification activity, and has been used as a traditional Chinese medicine to treat influenza for many years. Due to the complex chemical composition and diverse content of Jinyinhua, especially the many trace ingredients, the effective components are unknown. In this study, an improved two-dimensional high performance liquid chromatography-ultrafiltration combined with electrospray ionization-time-of-flight/mass spectroscopy (ESI-TOF/MS) approach was designed and used for the enrichment, screening and characterization of minor neuraminidase inhibitors in Jinyinhua. In the first dimension, semi-prep-HPLC was employed for the preliminary separation of different polarity components and enrichment of low content components from Jinyinhua extract. In the second dimension, hydrophilic interaction liquid chromatography and reverse phase-HPLC were used to separate the different polar fractions, respectively. The fractions then underwent ultrafiltration and ESI-TOF/MS for the comprehensive screening and characterization of potential neuraminidase inhibitors. As a result, a total of 44 compounds were found to have neuraminidase inhibitory activity, and 22 of these compounds were preliminarily identified by accurate molecular weight and UV absorption data compared with standards and references. The activity of 16 of these compounds was verified by the neuraminidase inhibition assay. This study provides support for the rapid screening of minor neuraminidase inhibitors from complex natural medicines.

Design, synthesis, bioactivity, and DFT calculation of 2-thiazolyl-hydrazone derivatives as influenza neuraminidase inhibitors

Three series of thiazolylhydrazone derivatives were designed, synthesized, and evaluated for their neuraminidase (NA) inhibitory activity against influenza virus H1N1 in vitro. Compounds 1 and 2 were synthesized via the one-pot reaction and compound 3 was synthesized in two steps. Pharmacological results showed that the majority of the target compounds 1, 2, and 3 exhibited moderate-to-good influenza NA inhibitory activity. The NA inhibitory activity of the most active compound 2g (IC50 = 7.12 μg/ml) is better than that of the lead compound A. Molecular docking was performed to study the possible interactions between compound 2g and the active site of NA. On the basis of biological results, a preliminary structure–activity relationship (SAR) was derived and discussed. Moreover, density functional theory (DFT) calculation was also performed to explain why the thiazolylhydrazone skeleton has NA inhibitory activity, especially compound 2g with the most potent inhibitory activity.

Antigenic drift originating from changes to the lateral surface of the neuraminidase head of influenza A virus.

Influenza viruses possess two surface glycoproteins, haemagglutinin and neuraminidase (NA). Although haemagglutinin plays a major role as a protective antigen, immunity to NA also contributes to protection. The NA protein consists of a stalk and a head portion, the latter of which possesses enzymatic NA (or sialidase) activity. Like haemagglutinin, NA is under immune pressure, which leads to amino acid alterations and antigenic drift. Amino acid changes accumulate around the enzymatic active site, which is located at the top of the NA head. However, amino acid alterations also accumulate at the lateral surface of the NA head. The reason for this accumulation remains unknown. Here, we isolated seven anti-NA monoclonal antibodies (mAbs) from individuals infected with A(H1N1)pdm09 virus. We found that amino acid mutations on the lateral surface of the NA head abolished the binding of all of these mAbs. All seven mAbs activated Fcγ receptor (FcγR)-mediated signalling pathways in effector cells and five mAbs possessed NA inhibition activity, but the other two did not; however, all seven protected mice from lethal challenge infection through their NA inhibition activity and/or FcγR-mediated antiviral activity. Serological analysis of individuals infected with A(H1N1)pdm09 virus revealed that some possessed or acquired the anti-NA-lateral-surface antibodies following infection. We also found antigenic drift on the lateral surface of the NA head of isolates from 2009 and 2015. Our results demonstrate that anti-lateral-surface mAbs without NA inhibition activity can provide protection by activating FcγR-mediated antiviral activity and can drive antigenic drift at the lateral surface of the NA head. These findings have implications for NA antigenic characterization in that they demonstrate that traditional NA inhibition assays are inadequate to fully characterize NA antigenicity.

Hemagglutinin Stalk-Reactive Antibodies Interfere with Influenza Virus Neuraminidase Activity by Steric Hindrance.

Hemagglutinin (HA) stalk-reactive antibodies are the basis of several current "one-shot" universal influenza vaccine efforts because they protect against a wide spectrum of influenza virus strains. The appreciated mechanism of protection by HA stalk-reactive antibodies is to inhibit HA stalk reconfiguration, blocking viral fusion and entry. This study shows that HA stalk-reactive antibodies also inhibit neuraminidase (NA) enzymatic activity, prohibiting viral egress. NA inhibition (NI) was evident for an attached substrate but not for unattached small-molecule cleavage of sialic acid. This finding suggests that the antibodies inhibit NA enzymatic activity through steric hindrance, thus limiting NA access to sialic acids when adjacent to HA on whole virions. Consistently, F(ab')2 fragments that occupied reduced area without loss of avidity or disrupted HA/NA interactions showed significantly reduced NI activity. Notably, HA stalk-binding antibodies lacking NI activity were unable to neutralize viral infection via microneutralization assays. This work suggests that NI activity is an important component of protection mediated by HA stalk-reactive antibodies.IMPORTANCE This study reports a new mechanism of protection mediated by influenza hemagglutinin stalk-reactive antibodies, i.e., inhibition of neuraminidase activity by steric hindrance, blocking access of neuraminidase to sialic acids when it abuts hemagglutinin on whole virions.

Utilization of Dianthus superbus L and its bioactive compounds for antioxidant, anti-influenza and toxicological effects

Dianthus superbus (DS) is a traditional medicinal herb well known for its medicinal and therapeutic potential and widely distributed in various Asian countries. The ethyl acetate (EA), butanol (Bu) and distilled water (DW) extracts of DS assessed for extraction of bioactive compounds and their biological activities. The chemical analysis was done using LC-MS/MS and antioxidant, anticancer and antiviral activities were determined. EA extracts showed strong anticancer activity with IC50 of 9.5, 13.8 and 69.9 μg/mL on SKOV, NCL-H1299 and Caski cancer cell lines, respectively. The Bu extracts exhibited strongest antiviral activity with respect to both influenza A and B viruses with IC50 values of 4.97 and 3.9 μg/mL, respectively. Also the metabolic profile for EA, Bu and DW extracts shows high variations and influence precisely the antioxidant, anticancer and antiviral properties. The quercetin 3- rutinoside and isorhamnetin 3- glucoside showed higher neuraminidase inhibition activity in dose dependent manner. Molecular docking study revealed that flavonol glycosides have higher binding activities towards influenza polymerase membrane glycoprotein. Correlation study showed that flavonol glycosides were linked to anti-influenza activity and cyclic peptides with anticancer activities. This study provides vital information for effective utilization of DS for medicinal, food and therapeutic purposes.

Design, synthesis and biological evaluation of honokiol derivatives as influenza neuraminidase inhibitors

Honokiol, a natural polyphenol, which was reported to have satisfactory influenza neuraminidase (NA) inhibitory activity, was structurally modified. Twenty-three compounds were synthesized and the ortho-effects in the epoxidation and hydrolyzation reactions were studied. The derivatives were evaluated for NA inhibitory activity and the benzoylhydrazone derivatives showed much better anti-NA activity than honokiol. Structure-activity relationship analysis suggested that the polyphenols exhibited better anti-NA activity than monophenols and biphenols. Furthermore, probable binding mode of drug with target revealed that the most active compound had much stronger interactions with the active site of NA than honokiol suggesting the potent anti-influenza virus activity.