Low-pH Stability of Influenza A Virus Sialidase Contributing to Virus Replication and Pandemic

Enhanced BSA Detection Precision: Leveraging High-Performance Dual-Gate Ion-Sensitive Field-Effect-Transistor Scheme and Surface-Treated Sensing Membranes

Bovine serum albumin (BSA) is commonly incorporated in vaccines to improve stability. However, owing to potential allergic reactions in humans, the World Health Organization (WHO) mandates strict adherence to a BSA limit (≤50 ng/vaccine). BSA detection with conventional techniques is time-consuming and requires specialized equipment. Efficient alternatives such as the ion-sensitive field-effect transistor (ISFET), despite rapid detection, affordability, and portability, do not detect BSA at low concentrations because of inherent sensitivity limitations. This study proposes a silicon-on-insulator (SOI) substrate-based dual-gate (DG) ISFET platform to overcome these limitations. The capacitive coupling DG structure significantly enhances sensitivity without requiring external circuits, owing to its inherent amplification effect. The extended-gate (EG) structure separates the transducer unit for electrical signal processing from the sensing unit for biological detection, preventing chemical damage to the transducer, accommodating a variety of biological analytes, and affording easy replaceability. Vapor-phase surface treatment with (3-Aminopropyl) triethoxysilane (APTES) and the incorporation of a SnO2 sensing membrane ensure high BSA detection efficiency and sensitivity (144.19 mV/log [BSA]). This DG-FET-based biosensor possesses a simple structure and detects BSA at low concentrations rapidly. Envisioned as an effective on-site diagnostic tool for various analytes including BSA, this platform addresses prior limitations in biosensing and shows promise for practical applications.

pH-dependent endocytosis mechanisms for influenza A and SARS-coronavirus

The ongoing SARS-CoV-2 pandemic and the influenza epidemics have revived the interest in understanding how these highly contagious enveloped viruses respond to alterations in the physicochemical properties of their microenvironment. By understanding the mechanisms and conditions by which viruses exploit the pH environment of the host cell during endocytosis, we can gain a better understanding of how they respond to pH-regulated anti-viral therapies but also pH-induced changes in extracellular environments. This review provides a detailed explanation of the pH-dependent viral structural changes preceding and initiating viral disassembly during endocytosis for influenza A (IAV) and SARS coronaviruses. Drawing upon extensive literature from the last few decades and latest research, I analyze and compare the circumstances in which IAV and SARS-coronavirus can undertake endocytotic pathways that are pH-dependent. While there are similarities in the pH-regulated patterns leading to fusion, the mechanisms and pH activation differ. In terms of fusion activity, the measured activation pH values for IAV, across all subtypes and species, vary between approximately 5.0 to 6.0, while SARS-coronavirus necessitates a lower pH of 6.0 or less. The main difference between the pH-dependent endocytic pathways is that the SARS-coronavirus, unlike IAV, require the presence of specific pH-sensitive enzymes (cathepsin L) during endosomal transport. Conversely, the conformational changes in the IAV virus under acidic conditions in endosomes occur due to the specific envelope glycoprotein residues and envelope protein ion channels (viroporins) getting protonated by H+ ions. Despite extensive research over several decades, comprehending the pH-triggered conformational alterations of viruses still poses a significant challenge. The precise mechanisms of protonation mechanisms of certain during endosomal transport for both viruses remain incompletely understood. In absence of evidence, further research is needed.

Possible bidirectional human-swine and subsequent human-human transmission of influenza virus A(H1N1)/2009 in Japan

In 2019, sows at a swine farm in Japan showed influenza-like illness (ILI) shortly after contact with an employee that exhibited ILI. Subsequently, a veterinarian became sick shortly after examining the sows and was diagnosed with influenza A virus (IAV) infection. Then, her family also contracted the infection. Subsequently, Pandemic A(H1N1)2009 viruses were isolated from all samples obtained from the sows, veterinarian and her family. Whole-genome analysis of the isolates confirmed that the viruses belonged to the same lineage (6B.1A) and the genome sequences obtained from all of the isolates were almost identical to each other. Furthermore, an epidemiological survey revealed no contact between veterinarians or their families and influenza patients prior to the onset of illness. These results strongly indicated a case of bidirectional infection between humans and sows. At the same time, we found a few unique mutations in the IAV genomes corresponding to the host species. The mutations that occurred in the virus after it was transferred from the farm worker to the sows were not observed in the humans infected from the sows, probably as a result of the mutations reverting to the original nucleotides. These results demonstrate that the bidirectional transmission of IAV is a potential risk for the next pandemic outbreak due to the emergence of new mutant strains.

An overview of influenza A virus genes, protein functions, and replication cycle highlighting important updates

The recent research findings on influenza A virus (IAV) genome biology prompted us to present a comprehensive overview of IAV genes, protein functions, and replication cycle. The eight gene segments of the IAV genome encode 17 proteins, each having unique functions contributing to virus fitness in the host. The polymerase genes are essential determinants of IAV pathogenicity and virulence; however, other viral components also play crucial roles in the IAV replication, transmission, and adaptation. Specific adaptive mutations within polymerase (PB2, PB1, and PA) and glycoprotein-hemagglutinin (HA) and neuraminidase (NA) genes, may facilitate interspecies transmission and adaptation of IAV. The HA-NA interplay is essential for establishing the IAV infection; the low pH triggers the inactivation of HA-receptor binding, leading to significantly lower NA activities, indicating that the enzymatic function of NA is dependent on HA binding. While the HA and NA glycoproteins are required to initiate infection, M1, M2, NS1, and NEP proteins are essential for cytoplasmic trafficking of viral ribonucleoproteins (vRNPs) and the assembly of the IAV virions. The mechanisms that enable IAV to exploit the host cell resources to advance the infection are discussed. A comprehensive understanding of IAV genome biology is essential for developing antivirals to combat the IAV disease burden.

Exploration of correlation of oral hygiene and condition with influenza infection

Influenza viruses are known to be infected through epithelial cells of the upper respiratory tract. The oral cavity is in close anatomical proximity to the upper respiratory tract, and it is conceivable that the viruses could pass through the oral cavity and infect to the upper respiratory tract. Several researchers have suggested that colonization of certain pathogenic bacteria such as Staphylococcus aureus or Streptococcus pneumoniae might affect the risk of influenza viral disease, indicating that oral hygiene and/or condition might play an important role in respiratory viral infection. Therefore, the purpose of this study was to investigate whether an oral hygiene/condition might impact influenza infection. We conducted a retrospective observational study of Japanese citizens' regional cohort (N = 2,904) consisting of National Health Insurance beneficiaries who underwent annual health/dental examination with data entries in the Kokuho database (KDB). Trained dentists checked the oral hygiene/condition, and saliva specimens were examined using the LION dental saliva multi-test (SMT) kit. Influenza infection was identified from the diagnosis recorded in the KDB. The correlations between influenza infection and oral hygiene, dryness of the mouth, or various salivary test results were examined by a multivariate analysis adjusting for confounding factors such as gender, age, recent smoking, alcohol drinking, BMI, HbA1c, RBC for influenza infection. The logistic regression model showed that age significantly correlated with influenza infection. In addition, oral hygiene status had a nearly significant impact on influenza infection (p = 0.061), whereby, the subjects with poor oral hygiene had a higher risk of influenza infection than those with good oral hygiene (odds ratio: 1.63, 95% confidence interval: 0.89-2.95). Further, the prevalence of influenza infection was lower in the subjects with saliva weakly acidic and/or containing higher protein level. The results of this study suggested that the maintenance of oral health conditions might be one of the pivotal factors for preventing and reducing influenza infection.

Analysis of the Evolution of Pandemic Influenza A(H1N1) Virus Neuraminidase Reveals Entanglement of Different Phenotypic Characteristics

The influenza A virus (IAV) neuraminidase (NA) is essential for virion release from cells and decoy receptors and an important target of antiviral drugs and antibodies. Adaptation to a new host sialome and escape from the host immune system are forces driving the selection of mutations in the NA gene. Phylogenetic analysis shows that until 2015, 16 amino acid substitutions in NA became fixed in the virus population after introduction in the human population of the pandemic IAV H1N1 (H1N1pdm09) in 2009. The accumulative effect of these substitutions, in the order in which they appeared, was analyzed using recombinant proteins and viruses in combination with different functional assays. The results indicate that NA activity did not evolve to a single optimum but rather fluctuated within a certain bandwidth. Furthermore, antigenic and enzymatic properties of NA were intertwined, with several residues affecting multiple properties. For example, the substitution K432E in the second sialic acid binding site, next to the catalytic site, was shown to affect catalytic activity, substrate specificity, and the pH optimum for maximum activity. This substitution also altered antigenicity of NA, which may explain its selection. We propose that the entanglement of NA phenotypes may be an important determining factor in the evolution of NA.IMPORTANCE Since its emergence in 2009, the pandemic H1N1 influenza A virus (IAV) has caused significant disease and mortality in humans. IAVs contain two envelope glycoproteins, the receptor-binding hemagglutinin (HA) and the receptor-destroying neuraminidase (NA). NA is essential for virion release from cells and decoy receptors, is an important target of antiviral drugs, and is increasingly being recognized as an important vaccine antigen. Not much is known, however, about the evolution of this protein upon the emergence of the novel pandemic H1N1 virus, with respect to its enzymatic activity and antigenicity. By reconstructing the evolutionary path of NA, we show that antigenic and enzymatic properties of NA are intertwined, with several residues affecting multiple properties. Understanding the entanglement of NA phenotypes will lead to better comprehension of IAV evolution and may help the development of NA-based vaccines.

Chloroquine to fight COVID-19: A consideration of mechanisms and adverse effects?

The COVID-19 outbreak emerged in December 2019 and has rapidly become a global pandemic. A great deal of effort has been made to find effective drugs against this disease. Chloroquine (CQ) and hydroxychloroquine (HCQ) were widely adopted in treating COVID-19, but the results were contradictive. CQ/HCQ have been used to prevent and treat malaria and are efficacious anti-inflammatory agents in rheumatoid arthritis and systemic lupus erythematosus. These drugs have potential broad-spectrum antiviral properties, but the underlying mechanisms are speculative. In this review, we re-evaluated the treatment outcomes and current hypothesis for the working mechanisms of CQ/HCQ as COVID-19 therapy with a special focus on disruption of Ca2+ signaling. In so doing, we attempt to show how the different hypotheses for CQ/HCQ action on coronavirus may interact and reinforce each other. The potential toxicity is also noted due to its action on Ca2+ and hyperpolarization-activated cyclic nucleotide-gated channels in cardiac myocytes and neuronal cells. We propose that intracellular calcium homeostasis is an alternative mechanism for CQ/HCQ pharmacology, which should be considered when evaluating the risks and benefits of therapy in these patients and other perspective applications.

Influenza Virus Neuraminidase Structure and Functions

With the constant threat of emergence of a novel influenza virus pandemic, there must be continued evaluation of the molecular mechanisms that contribute to virulence. Although the influenza A virus surface glycoprotein neuraminidase (NA) has been studied mainly in the context of its role in viral release from cells, accumulating evidence suggests it plays an important, multifunctional role in virus infection and fitness. This review investigates the various structural features of NA, linking these with functional outcomes in viral replication. The contribution of evolving NA activity to viral attachment, entry and release of virions from infected cells, and maintenance of functional balance with the viral hemagglutinin are also discussed. Greater insight into the role of this important antiviral drug target is warranted.

Functional analysis of glyco-molecules that bind with influenza virus

Influenza A virus (IAV) recognizes terminal sialic acid of sialoglyco-conjugates on host cells through the viral envelope glycoprotein hemagglutinin (HA), followed by initiation of entry into the cells. Molecular species of sialic acid are largely divided into two moieties: N-acetylneuraminic acid (Neu5Ac) and N-glycolylneuraminic acid (Neu5Gc). A receptor for IAV infection generally means Neu5Ac. Almost all equine IAVs and some human, swine, and duck IAVs bind not only to Neu5Ac but also to Neu5Gc. In nonhuman animals, Neu5Gc has been detected in swine and equine tracheas and the duck colon, which are the main replication sites of mammalian and avian IAVs. Therefore, Neu5Gc in these sites has been suggested to be a functional receptor for IAV infection. Humans cannot synthesize Neu5Gc due to a genetic defect of the Neu5Gc-synthesizing enzyme. We evaluated the receptor function of Neu5Gc in IAV infection in human cells. Our results indicated that Neu5Gc expression on the surface of human cells is not a functional receptor for IAV infection and that it has a negative effect on infectivity of IAV possessing Neu5Gc binding ability. IAV also binds to non-sialo 3-O-sulfated galactosylceramide (sulfatide). Sulfatide has been suggested to be a functional receptor for IAV infection. However, we have shown that sulfatide is not a functional receptor for IAV infection and that the binding of HA with sulfatide enhances progeny virus production. It is expected that functions of these glyco-molecules can be used in prevention and development of new drugs against IAV.