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[Display omitted] Enveloped viruses are pivotal in causing various illnesses, including influenza and COVID-19. The antimicrobial peptide LL-37, a critical part of the human innate immune system, exhibits potential as an antiviral agent capable of thwarting these viral threats. Its mode of action involves versatile and non-specific interactions that culminate in dismantling the viral envelope, ultimately rendering the viruses inert. However, the exact mechanism of action is not yet understood. Here, the mechanism of LL-37 triggered changes in the structure and function of an enveloped virus is investigated. The bacteriophage "Phi6" is used as a surrogate for pathogenic enveloped viruses. Small angle X-ray and neutron scattering combined with light scattering techniques demonstrate that LL-37 actively integrates into the virus's lipid envelope. LL-37 addition to Phi6 leads to curvature modification in the lipid bilayer, ultimately separating the envelope from the nucleocapsid. Additional biological assays confirm the loss of virus infectivity in the presence of LL-37, which coincides with the structural transformations. The results provide a fundamental understanding of the structure-activity relationship related to enveloped viruses. The knowledge of peptide-virus interactions can guide the design of future peptide-based antiviral drugs and therapies. [ABSTRACT FROM AUTHOR]

The causative pathogen of coronavirus disease 2019 (COVID‐19), severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2), is an enveloped virus assembled by a lipid envelope and multiple structural proteins. In this study, by integrating experimental data, structural modeling, as well as coarse‐grained and all‐atom molecular dynamics simulations, we constructed multiscale models of SARS‐CoV‐2. Our 500‐ns coarse‐grained simulation of the intact virion allowed us to investigate the dynamic behavior of the membrane‐embedded proteins and the surrounding lipid molecules in situ. Our results indicated that the membrane‐embedded proteins are highly dynamic, and certain types of lipids exhibit various binding preferences to specific sites of the membrane‐embedded proteins. The equilibrated virion model was transformed into atomic resolution, which provided a 3D structure for scientific demonstration and can serve as a framework for future exascale all‐atom molecular dynamics (MD) simulations. A short all‐atom molecular dynamics simulation of 255 ps was conducted as a preliminary test for large‐scale simulations of this complex system. [ABSTRACT FROM AUTHOR]

Monolaurin was utilized to formulate temperature-driven phase inversion nanoemulsions containing lesser galangal essential oil, fixed oil, and Cremophor RH40, with aim for eradicating enveloped viruses. Results showed that the droplet size of the nanoemulsion depended on lesser galangal essential oil–fixed oil ratio, monolaurin concentration, and oil concentration. Nanoemulsions prepared from lesser galangal essential oil–perilla oil (60:40) exhibited approximately 50-nm nanosized droplets and high entrapment efficiency (98.68 % ± 2.45 %). After storage at 25 °C for 1 year, droplet size did not vary significantly from the initial size, and monolaurin content was >95 %, indicating good physical and chemical stability. The monolaurin was located at the oil–water interface as indicated by a two-dimensional nuclear Overhauser effect nuclear magnetic resonance spectroscope and computer simulation. The 0.2% w/v monolaurin nanoemulsion inhibited SARS-CoV-2 and influenza A (H1N1) viruses with efficacy more than 3 log reduction (99.90 %) and low cytotoxicity. Hence, the monolaurin nanoemulsion can successfully eradicate enveloped viruses, especially SARS-CoV-2 and influenza A (H1N1).

Dengue virus (DENV) is one of the most prevalent arthropod-borne diseases. It may cause dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS), while no effective vaccines and drugs are available. Our study demonstrated that conessine exhibits broad antiviral activity against several enveloped viruses, including DENV, vesicular stomatitis virus, and herpes simplex virus. In addition, conessine has no direct destructive effect on the integrity or infectivity of virions. Both pre-treatment and post-treatment with conessine significantly reduce DENV replication. Pre-treatment with conessine disrupts the endocytosis of enveloped viruses, while post-treatment disturbs DENV RNA replication or translation at an early stage. Through screening differentially expressed genes by transcriptome sequencing, we found that conessine may affect cholesterol biosynthesis, metabolism or homeostasis. Finally, we confirmed that conessine inhibits virus replication through up-regulating cholesterol levels. Our work suggests that conessine could be developed as a prophylactic and therapeutic treatment for infectious diseases caused by enveloped viruses.

The endosomal sorting complex required for transport (ESCRT) is an essential molecular machinery in eukaryotic cells that facilitates the invagination of endosomal membranes, leading to the formation of multivesicular bodies (MVBs). It participates in various cellular processes, including lipid bilayer remodeling, cytoplasmic separation, autophagy, membrane fission and re-modeling, plasma membrane repair, as well as the invasion, budding, and release of certain enveloped viruses. The ESCRT complex consists of five complexes, ESCRT-0 to ESCRT-III and VPS4, along with several accessory proteins. ESCRT-0 to ESCRT-II form soluble complexes that shuttle between the cytoplasm and membranes, mainly responsible for recruiting and transporting membrane proteins and viral particles, as well as recruiting ESCRT-III for membrane neck scission. ESCRT-III, a soluble monomer, directly participates in vesicle scission and release, while VPS4 hydrolyzes ATP to provide energy for ESCRT-III complex disassembly, enabling recycling. Studies have confirmed the hijacking of ESCRT complexes by enveloped viruses to facilitate their entry, replication, and budding. Recent research has focused on the interaction between various components of the ESCRT complex and different viruses. In this review, we discuss how different viruses hijack specific ESCRT regulatory proteins to impact the viral life cycle, aiming to explore commonalities in the interaction between viruses and the ESCRT system. [ABSTRACT FROM AUTHOR]

Abstract Several approaches have been developed to analyze the entry of highly pathogenic viruses. In this study, we report the implementation of a Bimolecular Multicellular Complementation (BiMuC) assay to safely and efficiently monitor SARS-CoV-2 S-mediated membrane fusion without the need for microscopy-based equipment. Using BiMuC, we screened a library of approved drugs and identified compounds that enhance S protein-mediated cell-cell membrane fusion. Among them, ethynylestradiol promotes the growth of SARS-CoV-2 and Influenza A virus in vitro. Our findings demonstrate the potential of BiMuC for identifying small molecules that modulate the life cycle of enveloped viruses, including SARS-CoV-2.

ABSTRACT Ebola virus (EBOV) causes a hemorrhagic fever with fatality rates up to 90%. The EBOV entry process is complex and incompletely understood. Following attachment to host cells, EBOV is trafficked to late endosomes/lysosomes where its glycoprotein (GP) is processed to a 19-kDa form, which binds to the EBOV intracellular receptor Niemann-Pick type C1. We previously showed that the cathepsin protease inhibitor, E-64d, blocks infection by pseudovirus particles bearing 19-kDa GP, suggesting that further cathepsin action is needed to trigger fusion. This, however, has not been demonstrated directly. Since 19-kDa Ebola GP fusion occurs in late endosomes, we devised a system in which enriched late endosomes are used to prepare supported planar endosomal membranes (SPEMs), and fusion of fluorescent (pseudo)virus particles is monitored by total internal reflection fluorescence microscopy. We validated the system by demonstrating the pH dependencies of influenza virus hemagglutinin (HA)-mediated and Lassa virus (LASV) GP-mediated fusion. Using SPEMs, we showed that fusion mediated by 19-kDa Ebola GP is dependent on low pH, enhanced by Ca2+, and augmented by the addition of cathepsins. Subsequently, we found that E-64d inhibits full fusion, but not lipid mixing, mediated by 19-kDa GP, which we corroborated with the reversible cathepsin inhibitor VBY-825. Hence, we provide both gain- and loss-of-function evidence that further cathepsin action enhances the fusion activity of 19-kDa Ebola GP. In addition to providing new insights into how Ebola GP mediates fusion, the approach we developed employing SPEMs can now be broadly used for studies of virus and toxin entry through endosomes. IMPORTANCE Ebola virus is the causative agent of Ebola virus disease, which is severe and frequently lethal. EBOV gains entry into cells via late endosomes/lysosomes. The events immediately preceding fusion of the viral and endosomal membranes are incompletely understood. In this study, we report a novel in vitro system for studying virus fusion with endosomal membranes. We validated the system by demonstrating the low pH dependencies of influenza and Lassa virus fusion. Moreover, we show that further cathepsin B action enhances the fusion activity of the primed Ebola virus glycoprotein. Finally, this model endosomal membrane system should be useful in studying the mechanisms of bilayer breaching by other enveloped viruses, by non-enveloped viruses, and by acid-activated bacterial toxins.

In a framework aimed at the recovery and enhancement of medicinal plants endemic to the territory of the Cilento and Vallo di Diano National Park, Lavandula austroapennina N.G. Passal., Tundis and Upson has aroused interest. An insight into the chemical composition of the corolla, calyx, leaf, stem, and root organs was carried out following ultrasound-assisted maceration in n-hexane. The obtained lipophilic extracts were explored using ultra-high-performance chromatography coupled to high-resolution mass spectrometry (UHPLC-ESI-QqTOF-MS/MS). The extracts from the different organs varied in their relative content of fatty acids, ursanes, and oleanane-type triterpenes. In particular, the oleanolic acid content appeared to increase in the order of corolla < leaf < stem. An MTT assay was performed to verify the possible cytotoxicity of the organ extracts of L. austroapennina at a concentration ranging from 12.5 to 400 µg/mL on the Vero CCL-81 cell line. Antiviral activity against herpes simplex virus type 1 (HSV-1), alpha human coronavirus 229E (HCoV-229E), and poliovirus type 1 (PV-1) was evaluated via a plaque reduction assay in the same cellular model. All the extracts did not show cytotoxic effects after 2 and 24 h exposure times, and the antiviral efficacy was particularly important for the stem extract, capable of completely inhibiting the tested viruses at low doses. The antiviral activity in a non-enveloped virus PV-1 allowed the assertion that the extracts from the organs of L. austroapennina, and especially the stem extract, interfered directly with the viral envelope. This study underlines how much knowledge of a territory's medicinal plant heritage is a harbinger of promising discoveries in the health field. [ABSTRACT FROM AUTHOR]

Macrophages are critical in the pathogenesis of a diverse group of viral pathogens, both as targets of infection and for eliciting primary defense mechanisms. Our prior in vitro work identified that CD40 signaling in murine peritoneal macrophages protects against several RNA viruses by eliciting IL-12, which stimulates the production of interferon gamma (IFN-γ). Here, we examine the role of CD40 signaling in vivo. We show that CD40 signaling is a critical, but currently poorly appreciated, component of the innate immune response using two distinct infectious agents: mouse-adapted influenza A virus (IAV, PR8) and recombinant VSV encoding the Ebola virus glycoprotein (rVSV-EBOV GP). We find that stimulation of CD40 signaling decreases early IAV titers, whereas loss of CD40 elevated early titers and compromised lung function by day 3 of infection. Protection conferred by CD40 signaling against IAV is dependent on IFN-γ production, consistent with our in vitro studies. Using rVSV-EBOV GP that serves as a low-biocontainment model of filovirus infection, we demonstrate that macrophages are a CD40-expressing population critical for protection within the peritoneum and T-cells are the key source of CD40L (CD154). These experiments reveal the in vivo mechanisms by which CD40 signaling in macrophages regulates the early host responses to RNA virus infection and highlight how CD40 agonists currently under investigation for clinical use may function as a novel class of broad antiviral treatments. [ABSTRACT FROM AUTHOR]

Several approaches have been developed to analyze the entry of highly pathogenic viruses. In this study, we report the implementation of a Bimolecular Multicellular Complementation (BiMuC) assay to safely and efficiently monitor SARS-CoV-2 S-mediated membrane fusion without the need for microscopy-based equipment. Using BiMuC, we screened a library of approved drugs and identified compounds that enhance S protein-mediated cell-cell membrane fusion. Among them, ethynylestradiol promotes the growth of SARS-CoV-2 and Influenza A virus in vitro. Our findings demonstrate the potential of BiMuC for identifying small molecules that modulate the life cycle of enveloped viruses, including SARS-CoV-2. [ABSTRACT FROM AUTHOR]

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 pHsensitive 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. [ABSTRACT FROM AUTHOR]

The formation of membrane vesicles is a common feature in all eukaryotes. Lipid rafts are the best-studied example of membrane domains for both eukaryotes and prokaryotes, and their existence also is suggested in Archaea membranes. Lipid rafts are involved in the formation of transport vesicles, endocytic vesicles, exocytic vesicles, synaptic vesicles and extracellular vesicles, as well as enveloped viruses. Two mechanisms of how rafts are involved in vesicle formation have been proposed: first, that raft proteins and/or lipids located in lipid rafts associate with coat proteins that form a budding vesicle, and second, vesicle budding is triggered by enzymatic generation of cone-shaped ceramides and inverted cone-shaped lyso-phospholipids. In both cases, induction of curvature is also facilitated by the relaxation of tension in the raft domain. In this Review, we discuss the role of raft-derived vesicles in several intracellular trafficking pathways. We also highlight their role in different pathways of endocytosis, and in the formation of intraluminal vesicles (ILVs) through budding inwards from the multivesicular body (MVB) membrane, because rafts inside MVB membranes are likely to be involved in loading RNA into ILVs. Finally, we discuss the association of glycoproteins with rafts via the glycocalyx. [ABSTRACT FROM AUTHOR]

For decades, the ability of detergents to solubilize biological membranes has been utilized in biotechnological manufacturing to disrupt the lipid envelope of potentially contaminating viruses and thus enhance the safety margins of plasma- and cell-derived drugs. This ability has been linked to detergent micelles, which are formed if the concentration of detergent molecules exceeds the critical micelle concentration (CMC). Traditionally, the CMC of detergents is determined in deionized water (ddH2O), i.e., a situation considerably different from the actual situation of biotechnological manufacturing. This study compared, for five distinct detergents, the CMC in ddH2O side-by-side with two biopharmaceutical process intermediates relevant to plasma-derived (Immunoglobulin) and cell-derived (monoclonal antibody) products, respectively. Depending on the matrix, the CMC of detergents changed by a factor of up to ~4-fold. Further, the CMC in biotechnological matrices did not correlate with antiviral potency, as Triton X-100 (TX-100) and similar detergents had comparatively higher CMCs than polysorbate-based detergents, which are known to be less potent in terms of virus inactivation. Finally, it was demonstrated that TX-100 and similar detergents also have virus-inactivating properties if applied below the CMC. Thus, the presence of detergent micelles might not be an absolute prerequisite for the disruption of virus envelopes. [ABSTRACT FROM AUTHOR]

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.

Flaviviruses are enveloped viruses which include human pathogens that are predominantly transmitted by mosquitoes and ticks. Some, such as dengue virus, exhibit the phenomenon of antibody-dependent enhancement (ADE) of disease, making vaccine-based routes of fighting infections problematic. The pH-dependent conformational change of the envelope (E) protein required for fusion between the viral and endosomal membranes is an attractive point of inhibition by antivirals as it has the potential to diminish the effects of ADE. We examined six flaviviruses by employing large-scale molecular dynamics (MD) simulations of raft systems that represent a substantial portion of the flaviviral envelope. We utilised a benzene-mapping approach that led to a discovery of shared hotspots and conserved cryptic sites. A cryptic pocket previously shown to bind a detergent molecule exhibited strain-specific characteristics. An alternative conserved cryptic site at the E protein domain interfaces showed a consistent dynamic behaviour across flaviviruses and contained a conserved cluster of ionisable residues. Constant-pH simulations revealed cluster and domain-interface disruption under low pH conditions. Based on this, we propose a cluster-dependent mechanism that addresses inconsistencies in the histidine-switch hypothesis and highlights the role of cluster protonation in orchestrating the domain dissociation pivotal for the formation of the fusogenic trimer.

ABSTRACT The periodic emergence of infectious disease poses a serious threat to human life. Among the causative agents, including pathogenic bacteria and fungi, enveloped viruses have caused global pandemics. In the last 10 years, outbreaks of severe acute respiratory syndrome coronavirus 2 disease, severe acute respiratory syndrome, and Middle East respiratory syndrome have all been caused by enveloped viruses. Among several paths of secondary transmission, inhalation of aerosols containing saliva with sputum droplets from infected patients is the major path. To prevent these infectious diseases, mass use of antiviral agents is essential. The yeast-derived vacuole is a small organelle in which hydrolytic enzymes are concentrated. It is an intracellular organ with an excellent ability to process old organelles and bacteria and viruses that have invaded from the outside and can be present in sufficient quantity to be called a kind of enzyme bomb. We confirmed the inhibition of virus infection and structural collapse by vacuole treatment. Among several enzymes, proteases affected Phi6 infectivity. This study tried to isolate these vacuoles from yeast and use them as an antiviral agent for virus treatment, which is a recent issue. We confirmed that viral infectivity was inactivated, and structure collapsed through vacuole treatment. This paper is meaningful in that extracellularly isolated yeast-derived vacuoles are a first attempt to utilize vacuoles for viral treatment. IMPORTANCE The study assesses the vacuoles isolated from the yeast Saccharomyces cerevisiae as green antiviral agents to decrease the concerns about massive use of chemical antiviral agents and its side effects. To prevent the spreading of infectious diseases, personal or public use of antiviral agents is encouraged. The concern about the active compounds of these chemical antiviral agents has grown. Active compounds of antiviral agents have potential side effects on human health and the environment. Our proposed approach suggests effective and green antivirus material from a nonhazardous yeast strain. Also, large-scale production using a fermentation process can allow cost-effectiveness. The results showed sufficient reduced infectivity by vacuole treatment. The exposed vacuole can play the roles of both enzyme bomb to the virus and renewable nutrient source in the ecosystem.

The mosquito protein AEG12 encompasses a large (~ 3800 Å3) hydrophobic cavity which binds and delivers unsaturated fatty acids into biological membranes, allowing it to lyse cells and neutralize a wide range of enveloped viruses. Herein, the lytic and antiviral activities are modified with non‐naturally occurring lipid ligands. We generated novel AEG12 complexes in which the endogenous fatty acid ligands were replaced with hydrophobic viral inhibitors. The resulting compounds modulated cytotoxicity and infectivity against SARS‐CoV‐2, potentially reflecting additional mechanisms of action beyond membrane destabilization. These studies provide valuable insight into the design of novel broad‐spectrum antiviral therapeutics centred on the AEG12 protein scaffold as a delivery vehicle for hydrophobic therapeutic compounds. [ABSTRACT FROM AUTHOR]

Several studies recently highlighted the role of lipoprotein receptors in viral entry. These receptors are evolutionarily ancient proteins, key for the transport of lipids as well as other signaling molecules across the plasma membrane. Here, we discuss the different families of lipoprotein receptors and how they are hijacked by enveloped viruses to promote their entry into infected cells. While the usage of lipoprotein receptors was known for members of the Flaviviridae family and vesicular stomatitis virus, the last 4 years have seen the discovery that these receptors are used by many genetically unrelated viruses. We also emphasize how viral particles interact with these receptors and the possible targeting of these host factors as antiviral strategies., Competing Interests: Conflict of interest The authors declare that they have no conflicts of interest with the contents of this article., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Aims: The dosages and efficacy of 14 ultraviolet (UV) decontamination technologies were measured against a SARS-CoV-2 surrogate virus that was dried onto different materials for laboratory and field testing.Methods and results: A live enveloped, ribonucleic acid (RNA) virus surrogate for SARS-CoV-2 was dried on stainless steel 304 (SS304), Navy Top Coat-painted SS304 (NTC), cardboard, polyurethane, polymethyl methacrylate (PMMA), and acrylonitrile butadiene styrene (ABS) materials at > 8.0 log10 plaque-forming units (PFU) per test coupon. The coupons were then exposed to UV radiation during both laboratory and field testing. Commercial and prototype UV-emitting devices were measured for efficacy: four handheld devices, three room/surface-disinfecting machines, five air disinfection devices, and two larger custom-made machines. UV device dosages ranged from 0.01 to 729 mJ cm−2. The antiviral efficacy among the different UV devices ranged from no decontamination up to nearly achieving sterilization. Importantly, cardboard required far greater dosage than SS304.Conclusion: Enormous variability in dosage and efficacy was measured among the different UV devices. Porous materials limit the utility of UV decontamination.Significance and impact of the study: UV devices have wide variability in dosages, efficacy, hazards, and UV output over time, indicating that each UV device needs independent technical measurement and assessment for product development prior to and during use.

Macrophages are critical in the pathogenesis of a diverse group of viral pathogens, both as targets of infection and for eliciting primary defense mechanisms. Our prior in vitro work identified that CD40 signaling in murine peritoneal macrophages protects against several RNA viruses by eliciting IL-12, which stimulates the production of interferon gamma (IFN-γ). Here, we examine the role of CD40 signaling in vivo. We show that CD40 signaling is a critical, but currently poorly appreciated, component of the innate immune response using two distinct infectious agents: mouse-adapted influenza A virus (IAV, PR8) and recombinant VSV encoding the Ebola virus glycoprotein (rVSV-EBOV GP). We find that stimulation of CD40 signaling decreases early IAV titers, whereas loss of CD40 elevated early titers and compromised lung function by day 3 of infection. Protection conferred by CD40 signaling against IAV is dependent on IFN-γ production, consistent with our in vitro studies. Using rVSV-EBOV GP that serves as a low-biocontainment model of filovirus infection, we demonstrate that macrophages are a CD40-expressing population critical for protection within the peritoneum and T-cells are the key source of CD40L (CD154). These experiments reveal the in vivo mechanisms by which CD40 signaling in macrophages regulates the early host responses to RNA virus infection and highlight how CD40 agonists currently under investigation for clinical use may function as a novel class of broad antiviral treatments.

In the last decades, the interest in seaweed has significantly increased. Bioactive compounds from seaweed's currently receive major attention from pharmaceutical companies as they express several interesting biological activities which are beneficial for humans. The structural diversity of seaweed metabolites provides diverse biological activities which are expressed through diverse mechanisms of actions. This review mainly focuses on the antiviral activity of seaweed's extracts, highlighting the mechanisms of actions of some seaweed molecules against infection caused by different types of enveloped viruses: influenza, Lentivirus (HIV-1), Herpes viruses, and coronaviruses. Seaweed metabolites with antiviral properties can act trough different pathways by increasing the host's defense system or through targeting and blocking virus replication before it enters host cells. Several studies have already established the large antiviral spectrum of seaweed's bioactive compounds. Throughout this review, antiviral mechanisms and medical applications of seaweed's bioactive compounds are analyzed, suggesting seaweed's potential source of antiviral compounds for the formulation of novel and natural antiviral drugs. [ABSTRACT FROM AUTHOR]

ABSTRACT Baculovirus is a powerful tool for biological control in agriculture and foreign gene expression and delivery in insect and mammalian cells. Baculovirus enters host cells by multiple endocytic pathways; however, the current understanding of the Bombyx mori nucleopolyhedrovirus (BmNPV) entry mechanism remains limited. Previous studies have identified NPC1 and NPC2 as important host factors for viral infection in insect cells, although their exact role in viral infection has not yet been determined. In this study, we demonstrate that the BmNPC1 protein is an important intracellular factor for BmNPV escape from the endosomal compartment, and the expression of BmNPC1 in Sf9 cells confers the virus the ability to enter into the nucleus of Sf9 cells. Additionally, the second luminal domain of BmNPC1 (BmNPC1-C) binds to the viral glycoprotein gp64, and preincubation of BmNPV with purified BmNPC1-C inhibits virus infection. Furthermore, knockout of the BmNPC2 protein results in reduced efficiency of viral fusion with the endosomal membrane, and BmNPC2 protein interacts directly with both viral envelope glycoprotein gp64 and the host BmNPC1 protein. BmNPC2 was found to be incorporated into progeny viral particles. Taken together, our results suggest that NPC2 protein incorporated into viral particles may facilitate viral infection through promoting the interaction of BmNPV and NPC1 in the endosome, thus enhancing viral fusion and escape from endosomes. These results, combined with those from previous studies, support that BmNPV hijacks two important cholesterol receptor members (NPC1 and NCP2) in the cholesterol intracellular transport pathway for viral entry into host cells. IMPORTANCE Baculovirus is an important biological factor for controlling insect populations and represents a powerful biological tool for gene delivery and expression. However, the host receptor of baculovirus is still unknown. In this study, we demonstrate that BmNPC1 protein is an important intracellular factor for BmNPV escape from the endosomal compartment, and the expression of BmNPC1 confers the ability of virus to enter into the host cell nucleus in nonpermissive Sf9 cells. BmNPC2 can bind to the virus and promote progeny virion infection through the NPC1-NPC2 endosome cholesterol transport pathway. We believe that our study on the BmNPV entry mechanism will further facilitate the application of baculovirus systems in eukaryotic gene delivery. Not only can the cholesterol transport pathway NPC1 protein be used by a variety of enveloped viruses, but the NPC2 protein can also be used by viruses to infect host cells. This will provide new insights into the study of enveloped virus infection mechanisms.

Growing concerns regarding the emergence of highly transmissible viral diseases highlight the urgent need to expand the repertoire of antiviral therapeutics. For this reason, new strategies for neutralizing and inhibiting these viruses are necessary. A promising approach involves targeting the glycans present on the surfaces of enveloped viruses. Lectins, known for their ability to recognize specific carbohydrate molecules, offer the potential for glycan-targeted antiviral strategies. Indeed, numerous studies have reported the antiviral effects of various lectins of both endogenous and exogenous origins. However, many lectins in their natural forms, are not suitable for use as antiviral therapeutics due to toxicity, other unfavorable pharmacological effects, and/or unreliable manufacturing sources. Therefore, improvements are crucial for employing lectins as effective antiviral therapeutics. A novel approach to enhance lectins' suitability as pharmaceuticals could be the generation of recombinant lectin-Fc fusion proteins, termed "lectibodies." In this review, we discuss the scientific rationale behind lectin-based antiviral strategies and explore how lectibodies could facilitate the development of new antiviral therapeutics. We will also share our perspective on the potential of these molecules to transcend their potential use as antiviral agents. [ABSTRACT FROM AUTHOR]

Phycoremediation of swine wastewater is a promising treatment since it efficiently removes nutrients and contaminants and, simultaneously, its biomass can be harvested and used to obtain a wide range of valuable compounds and metabolites. In this context, biomass microalgae were investigated for the phycoremediation of swine wastewater, and biomass extracts for its virucidal effect against enveloped and non-enveloped viruses. Microalgae were cultivated in a pilot scale bioreactor fed with swine wastewater as the growth substrate. Hexane, dichloromethane, and methanol were used to obtain the microalgae extracts. Extracts were tested for virucidal potential against HSV-1 and HAdV-5. Virucidal assays were conducted at temperatures that emulate environmental conditions (21 °C) and body temperature (37 °C). The maximum production of microalgae biomass reached a concentration of 318.5 ± 23.6 mgDW L−1. The results showed that phycoremediation removed 100% of ammonia-N and phosphate-P, with rates (k1) of 0.218 ± 0.013 and 0.501 ± 0.038 (day−1), respectively. All microalgae extract reduced 100% of the infectious capacity of HSV-1. The microalgae extracts with dichloromethane and methanol showed inhibition activities at the lowest concentration (3.125 µg mL−1). Virucidal assays against HAdV-5 using microalgae extract of hexane and methanol inhibited the infectious capacity of the virus by 70% at all concentrations tested at 37 °C. At a concentration of 12.5 µg mL−1, the dichloromethane microalgae extract reduced 50–80% of the infectious capacity of HAdV-5, also at 37 °C. Overall, the results suggest that the microalgae can be an attractive source of feedstock biomass for the exploration of alternative virucidal compounds. [ABSTRACT FROM AUTHOR]

In recent years, infectious diseases caused by viral infections have seriously endangered human health, especially COVID-19, caused by SARS-CoV-2, which continues to spread worldwide. The development of broad-spectrum antiviral inhibitors is urgently needed. Here, we report a series of small-molecule compounds that proved effective against human coronaviruses (HCoV), such as SARS-CoV-2 and its variants of concern (VOCs), including Alpha (B.1.1.7), Beta (B.1.351), Gamma (P.1), Delta (B.1.617.2), and Omicron (B.1.1.529), SARS-CoV, MERS-CoV, HCoV-OC43, and other viruses with class I viral fusion proteins, such as influenza virus, Ebola virus (EBOV), Nipah virus (NiV), and Lassa fever virus (LASV). They are also effective against class II enveloped viruses represented by ZIKV and class III enveloped viruses represented by vesicular stomatitis virus (VSV). Further studies have shown that these compounds may exert antiviral effects through a variety of mechanisms, including inhibiting the formation of the six-helix bundle, which is a typical feature of enveloped virus fusion with cell membranes, and/or targeting viral membrane to inactivate cell-free virions. These compounds are expected to become drug candidates against SARS-CoV-2 and other enveloped viruses. [ABSTRACT FROM AUTHOR]

Different light-based strategies have been investigated to inactivate viruses. Herein, we developed an HIV-based pseudotyped model of SARS-CoV-2 (SC2) to study the mechanisms of virus inactivation by using two different strategies; photoinactivation (PI) by UV-C light and photodynamic inactivation (PDI) by Photodithazine photosensitizer (PDZ). We used two pseudoviral particles harboring the Luciferase-IRES-ZsGreen reporter gene with either a SC2 spike on the membrane or without a spike as a naked control pseudovirus. The mechanism of viral inactivation by UV-C and PDZ-based PDI were studied via biochemical characterizations and quantitative PCR on four levels; free-cell viral damage; viral cell entry; DNA integration; and expression of reporter genes. Both UV-C and PDZ treatments could destroy single stranded RNA (ssRNA) and the spike protein of the virus, with different ratios. However, the virus was still capable of binding and entering into the HEK 293T cells expressing angiotensin-converting enzyme 2 (ACE-2). A dose-dependent manner of UV-C irradiation mostly damages the ssRNA, while PDZ-based PDI mostly destroys the spike and viral membrane in concentration and dose-dependent manners. We observed that the cells infected by the virus and treated with either UV-C or PDZ-based PDI could not express the luciferase reporter gene, signifying the viral inactivation, despite the presence of RNA and DNA intact genes. [ABSTRACT FROM AUTHOR]

There are many issues in the evaluation protocols based on CT (mg min/L) values, which have been used to assess the germicidal effect of highly oxidative and unstable ozonated water. The major problems include the carryover of culture medium components in virus inactivation assays and the reaction volume ratio between the virus suspension and ozonated water. Furthermore, it is essential to correct the CT value with the decay curve of dissolved ozone under the same conditions as the inactivation assay. In this study, these concerns were reexamined to obtain quantitative CT values. Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) inactivation test using ozonated water prepared from pure water was assessed by determining the corrected concentration time (CCT) values. Moreover, a possible inactivation mechanism of SARS-CoV-2 was discussed with the aid of findings from this study and previous reports. The findings revealed that the CCT value required for 99.95% inactivation of SARS-CoV-2 with ozonated water was 0.97 mg·min/L. To quantitatively evaluate the SARS-CoV-2 inactivation test, the virus purification procedure during the pretreatment and the CT value correction using a dissolved ozone decay curve obtained under the same condition as the inactivation test were demonstrated to be essential. We proposed a possible mechanism of SARS-CoV-2 inactivation with ozonated water. Amino acids such as tyrosine, tryptophan, methionine, cysteine, and histidine in the SARS-CoV-2 spike protein are susceptible to oxidative attack by the ozone dissolved in water. This attack may induce structural destruction of the spike protein and inhibit its binding to the angiotensin converting enzyme 2 (ACE2) receptor, an essential host receptor for viral infection, resulting in viral inactivation and contributing to infection suppression. [ABSTRACT FROM AUTHOR]

Fomites can represent a reservoir for pathogens, which may be subsequently transferred from surfaces to skin. In this study, we aim to understand how different factors (including virus type, surface type, time since last hand wash, and direction of transfer) affect virus transfer rates, defined as the fraction of virus transferred, between fingerpads and fomites. To determine this, 360 transfer events were performed with 20 volunteers using Phi6 (a surrogate for enveloped viruses), MS2 (a surrogate for nonenveloped viruses), and three clean surfaces (stainless steel, painted wood, and plastic). Considering all transfer events (all surfaces and both transfer directions combined), the mean transfer rates of Phi6 and MS2 were 0.17 and 0.26, respectively. Transfer of MS2 was significantly higher than that of Phi6 (P < 0.05). Surface type was a significant factor that affected the transfer rate of Phi6: Phi6 is more easily transferred to and from stainless steel and plastic than to and from painted wood. Direction of transfer was a significant factor affecting MS2 transfer rates: MS2 is more easily transferred from surfaces to fingerpads than from fingerpads to surfaces. Data from these virus transfer events, and subsequent transfer rate distributions, provide information that can be used to refine quantitative microbial risk assessments. This study provides a large-scale data set of transfer events with a surrogate for enveloped viruses, which extends the reach of the study to the role of fomites in the transmission of human enveloped viruses like influenza and SARS-CoV-2. [ABSTRACT FROM AUTHOR]

Influenza A virus matrix protein 1 (M1) is the most abundant protein within virions and functions at multiple steps of the virus life cycle, including nuclear RNA export, virus particle assembly, and virus disassembly. Two recent publications have presented the first structures of full‐length M1 and show that it assembles filaments in vitro via an interface between the N‐ and C‐terminal domains of adjacent monomers. These filaments were found to be similar to those that form the endoskeleton of assembled virions. The structures provide a molecular basis to understand the functions of M1 during the virus life cycle. Here, we compare and discuss the two structures, and explore their implications for the mechanisms by which the multifunctional M1 protein can mediate virus assembly, interact with viral ribonucleoproteins and act during infection of a new cell. [ABSTRACT FROM AUTHOR]

Several independent datasets suggest blood type A is over-represented and type O under-represented among COVID-19 patients. However, blood group antigens appear not to be conventional susceptibility factors in that they do not affect disease severity, and the relative risk to non-O individuals is attenuated when population prevalence is high. Here, I model a scenario in which ABO transfusion incompatibility reduces the chance of a patient transmitting the virus to an incompatible recipient – thus in Western populations type A and AB individuals are “super-recipients” while type O individuals are “super-spreaders”. This results in an offset in the timing of the epidemic among individuals of different blood types, and an increased relative risk to type A/AB patients that is most pronounced during early stages of the epidemic. However, once the majority of any given population is infected, the relative risk to each blood type approaches unity. Published data on COVID-19 prevalence from regions in the early stages of the SARS-CoV-2 epidemic suggests that if this model holds true, ABO incompatibility reduces virus transmissibility by at least 60 %. Exploring the implications of this model for vaccination strategies shows that paradoxically, targeted vaccination of either high-susceptibility type A/AB or “super-spreader” type O individuals is less effective than random vaccination at blocking community spread of the virus. Instead, the key is to maintain blood type diversity among the remaining susceptible individuals. Given the good agreement between this model and observational data on disease prevalence, the underlying biochemistry urgently requires experimental investigation.

In the last decades, the interest in seaweed has significantly increased. Bioactive compounds from seaweed’s currently receive major attention from pharmaceutical companies as they express several interesting biological activities which are beneficial for humans. The structural diversity of seaweed metabolites provides diverse biological activities which are expressed through diverse mechanisms of actions. This review mainly focuses on the antiviral activity of seaweed’s extracts, highlighting the mechanisms of actions of some seaweed molecules against infection caused by different types of enveloped viruses: influenza, Lentivirus (HIV-1), Herpes viruses, and coronaviruses. Seaweed metabolites with antiviral properties can act trough different pathways by increasing the host’s defense system or through targeting and blocking virus replication before it enters host cells. Several studies have already established the large antiviral spectrum of seaweed’s bioactive compounds. Throughout this review, antiviral mechanisms and medical applications of seaweed’s bioactive compounds are analyzed, suggesting seaweed’s potential source of antiviral compounds for the formulation of novel and natural antiviral drugs.

Animal viruses are parasites of animal cells that have characteristics such as heredity and replication. Viruses can be divided into non-enveloped and enveloped viruses if a lipid bilayer membrane surrounds them or not. All the membrane proteins of enveloped viruses that function in attachment to target cells or membrane fusion are modified by glycosylation. Glycosylation is one of the most common post-translational modifications of proteins and plays an important role in many biological behaviors, such as protein folding and stabilization, virus attachment to target cell receptors and inhibition of antibody neutralization. Glycans of the host receptors can also regulate the attachment of the viruses and then influence the virus entry. With the development of glycosylation research technology, the research and development of novel virus vaccines and antiviral drugs based on glycan have received increasing attention. Here, we review the effects of host glycans and viral proteins on biological behaviors of viruses, and the opportunities for prevention and treatment of viral infectious diseases.

Animal viruses are parasites of animal cells that have characteristics such as heredity and replication. Viruses can be divided into non-enveloped and enveloped viruses if a lipid bilayer membrane surrounds them or not. All the membrane proteins of enveloped viruses that function in attachment to target cells or membrane fusion are modified by glycosylation. Glycosylation is one of the most common post-translational modifications of proteins and plays an important role in many biological behaviors, such as protein folding and stabilization, virus attachment to target cell receptors and inhibition of antibody neutralization. Glycans of the host receptors can also regulate the attachment of the viruses and then influence the virus entry. With the development of glycosylation research technology, the research and development of novel virus vaccines and antiviral drugs based on glycan have received increasing attention. Here, we review the effects of host glycans and viral proteins on biological behaviors of viruses, and the opportunities for prevention and treatment of viral infectious diseases. [ABSTRACT FROM AUTHOR]

The entry of enveloped virus requires the fusion of viral and host cell membranes. An effective fusion inhibitor aiming at impeding such membrane fusion may emerge as a broad‐spectrum antiviral agent against a wide range of viral infections. Mycobacterium survives inside the phagosome by inhibiting phagosome–lysosome fusion with the help of a coat protein coronin 1. Structural analysis of coronin 1 and other WD40‐repeat protein suggest that the trp‐asp (WD) sequence is placed at distorted β‐meander motif (more exposed) in coronin 1. The unique structural feature of coronin 1 was explored to identify a simple lipo‐peptide sequence (myr‐WD), which effectively inhibits membrane fusion by modulating the interfacial order, water penetration, and surface potential. The mycobacterium inspired lipo‐dipeptide was successfully tested to combat type 1 influenza virus (H1N1) and murine coronavirus infections as a potential broad‐spectrum antiviral agent. [ABSTRACT FROM AUTHOR]

Featured Application: Biodegradable composite biomaterials with antimicrobial properties. The World Health Organization has called for new effective and affordable alternative antimicrobial materials for the prevention and treatment of microbial infections. In this regard, calcium alginate has previously been shown to possess antiviral activity against the enveloped double-stranded DNA herpes simplex virus type 1. However, non-enveloped viruses are more resistant to inactivation than enveloped ones. Thus, the viral inhibition capacity of calcium alginate and the effect of adding a low amount of carbon nanofibers (0.1% w/w) were explored here against a non-enveloped double-stranded DNA virus model for the first time. The results of this study showed that neat calcium alginate films partly inactivated this type of non-enveloped virus and that including that extremely low percentage of carbon nanofibers (CNFs) significantly enhanced its antiviral activity. These calcium alginate/CNFs composite materials also showed antibacterial properties against the Gram-positive Staphylococcus aureus bacterial model and no cytotoxic effects in human keratinocyte HaCaT cells. Since alginate-based materials have also shown antiviral activity against four types of enveloped positive-sense single-stranded RNA viruses similar to SARS-CoV-2 in previous studies, these novel calcium alginate/carbon nanofibers composites are promising as broad-spectrum antimicrobial biomaterials for the current COVID-19 pandemic. [ABSTRACT FROM AUTHOR]

Different light-based strategies have been investigated to inactivate viruses. Herein, we developed an HIV-based pseudotyped model of SARS-CoV-2 (SC2) to study the mechanisms of virus inactivation by using two different strategies; photoinactivation (PI) by UV-C light and photodynamic inactivation (PDI) by Photodithazine photosensitizer (PDZ). We used two pseudoviral particles harboring the Luciferase-IRES-ZsGreen reporter gene with either a SC2 spike on the membrane or without a spike as a naked control pseudovirus. The mechanism of viral inactivation by UV-C and PDZ-based PDI were studied via biochemical characterizations and quantitative PCR on four levels; free-cell viral damage; viral cell entry; DNA integration; and expression of reporter genes. Both UV-C and PDZ treatments could destroy single stranded RNA (ssRNA) and the spike protein of the virus, with different ratios. However, the virus was still capable of binding and entering into the HEK 293T cells expressing angiotensin-converting enzyme 2 (ACE-2). A dose-dependent manner of UV-C irradiation mostly damages the ssRNA, while PDZ-based PDI mostly destroys the spike and viral membrane in concentration and dose-dependent manners. We observed that the cells infected by the virus and treated with either UV-C or PDZ-based PDI could not express the luciferase reporter gene, signifying the viral inactivation, despite the presence of RNA and DNA intact genes.

• Computational methods integrating experimental data help elucidate viral life cycle. • Viruses are dynamic and have complex interactions with a variety of host factors. • We can now model the complex interplay of proteomic and genomic components. • Molecular biology, genomics, and computation complement structural methods. Enveloped viruses such as the flaviviruses represent a significant burden to human health around the world, with hundreds of millions of people each year affected by dengue alone. In an effort to improve our understanding of the molecular basis for the infective mechanisms of these viruses, extensive computational modelling approaches have been applied to elucidate their conformational dynamics. Multiscale protocols have been developed to simulate flavivirus envelopes in close accordance with biophysical data, in particular derived from cryo-electron microscopy, enabling high-resolution refinement of their structures and elucidation of the conformational changes associated with adaptation both to host environments and to immunological factors such as antibodies. Likewise, integrative modelling efforts combining data from biophysical experiments and from genome sequencing with chemical modification are providing unparalleled insights into the architecture of the previously unresolved nucleocapsid complex. Collectively, this work provides the basis for the future rational design of new antiviral therapeutics and vaccine development strategies targeting enveloped viruses. [ABSTRACT FROM AUTHOR]

Attachment of a virus with a specific receptor on the cell surface is the first and foremost step in virus infection. In case of enveloped viruses, their interaction with the host cell receptor is mediated by viral encoded glycoproteins on its envelope, a host derived lipid bilayer. Since, virus entry is a multistep process, after receptor recognition, envelope proteins mediate internalisation of virus particles into the host cell. Envelope glycoproteins are the first proteins that the host immune system encounters upon infection. Thus, envelope proteins are important drug target with multiple strategies to inhibit entry of the virus into the host. Currently, there are very few drugs that function as envelope protein inhibitors which are approved for human use. Here, we reviewed different classes of envelope proteins of various viruses and emphasised the use of small molecules to inhibit fusion of envelope proteins. Based on the available information in the literature, envelope proteins can be important drug targets and small molecules inhibitors can serve as potential antiviral drugs to block viral infection at an initial stage. [ABSTRACT FROM AUTHOR]

Abstract The development of self-disinfectant devices is highly needed to prevent and control infections, mainly caused by virus. In the past years, coronaviruses have been a threat to humanity, causing severe epidemics of respiratory infections such as severe acute respiratory syndrome (SARS), in 2003, and Middle East respiratory syndrome (MERS) in 2012, and presently the SARS-CoV2 is causing the COVID-19 pandemic. Previous studies have demonstrated that surface contamination play a significant role in the spreading of viruses. These studies demonstrated that the production of highly reactive species by copper alloys contributes to rapid elimination of viruses. Nanostructured materials such as semiconductors TiO2, Co3O4 CuO, NiO, and TiO2, and silver nanoparticles can decrease the virus viability on the surfaces when associated with polymers and textiles, especially in conditions of light exposure. In addition, graphene oxide is rising as a promising material for inactivation of viruses due to its capacity of destroying the viral envelope and capsid. The virucidal property of these materials can be enhanced by increasing their functionalization with photosensitizers. The present mini-review brings subsidies for the development of new advanced self-disinfectant materials that can be used in the manufacture of gloves, masks, and a variety of other devices.

Aims: To develop infectious (live/dead) enveloped virus test indicators and response surface methodology (RSM) models that evaluate survival of an enveloped ribonucleic acid (RNA) virus on contaminated aircraft materials after exposure to hot, humid air (HHA).Methods and Results: Enveloped RNA bacteriophage Phi6 (Φ6) was dried on wiring insulation, aircraft performance coating (APC), polypropylene, and nylon at ≥ 8 log10 plaque-forming units (PFU) test coupon−1. Only 2.4 log10 inactivation was measured on APC at 70°Celsius (°C), 5% relative humidity (RH) after 24 h. In contrast, HHA RSM models showed a 90% probability of a 7 log10 inactivation at ≥63°C, 90% RH after 1 h, and decontamination kinetics were similar across different materials. HHA decontamination of C-130 and C-17 aircraft showed >7 log10 and ≥5.9 log10 inactivation of enveloped virus on 100 and 110 test indicators, respectively, with a 1-h treatment, excluding ramp-up and ramp-down times.Conclusions: Enveloped RNA virus test indicators were successfully developed, lab tested for HHA decontamination, analyzed for RSM, and field-tested in aircraft demonstrations.Significance and Impact of the Study: The utility of HHA decontamination was demonstrated after inactivating enveloped RNA virus on aircraft with a 1-h HHA treatment within aircraft temperature and RH limits.

ABSTRACT Quantum dots (QDs) possess optical properties of superbright fluorescence, excellent photostability, narrow emission spectra, and optional colors. Labeled with QDs, single molecules/viruses can be rapidly and continuously imaged for a long time, providing more detailed information than when labeled with other fluorophores. While they are widely used to label proteins in single-molecule-tracking studies, QDs have rarely been used to study virus infection, mainly due to a lack of accepted labeling strategies. Here, we report a general method to mildly and readily label enveloped viruses with QDs. Lipid-biotin conjugates were used to recognize and mark viral lipid membranes, and streptavidin-QD conjugates were used to light them up. Such a method allowed enveloped viruses to be labeled in 2 h with specificity and efficiency up to 99% and 98%, respectively. The intact morphology and the native infectivity of viruses were preserved. With the aid of this QD labeling method, we lit wild-type and mutant Japanese encephalitis viruses up, tracked their infection in living Vero cells, and found that H144A and Q258A substitutions in the envelope protein did not affect the virus intracellular trafficking. The lipid-specific QD labeling method described in this study provides a handy and practical tool to readily “see” the viruses and follow their infection, facilitating the widespread use of single-virus tracking and the uncovering of complex infection mechanisms. IMPORTANCE Virus infection in host cells is a complex process comprising a large number of dynamic molecular events. Single-virus tracking is a versatile technique to study these events. To perform this technique, viruses must be fluorescently labeled to be visible to fluorescence microscopes. The quantum dot is a kind of fluorescent tag that has many unique optical properties. It has been widely used to label proteins in single-molecule-tracking studies but rarely used to study virus infection, mainly due to the lack of an accepted labeling method. In this study, we developed a lipid-specific method to readily, mildly, specifically, and efficiently label enveloped viruses with quantum dots by recognizing viral envelope lipids with lipid-biotin conjugates and recognizing these lipid-biotin conjugates with streptavidin-quantum dot conjugates. It is not only applicable to normal viruses, but also competent to label the key protein-mutated viruses and the inactivated highly virulent viruses, providing a powerful tool for single-virus tracking.

Infectious diseases caused by human immunodeficiency virus (HIV) and other highly pathogenic enveloped viruses, have threatened the global public health. Most antiviral drugs act as passive defenders to inhibit viral replication inside the cell, while a few of them function as gate keepers to combat viruses outside the cell, including fusion inhibitors, e.g., enfuvirtide, and receptor antagonists, e.g., maraviroc, as well as virus inactivators (including attachment inhibitors). Different from fusion inhibitors and receptor antagonists that must act in the presence of target cells, virus inactivators can actively inactivate cell-free virions in the blood, through interaction with one or more sites in the envelope glycoproteins (Envs) on virions. Notably, a number of protein- and peptide-based virus inactivators (PPVIs) under development are expected to have a better utilization rate than the current antiviral drugs and be safer for in vivo human application than the chemical-based virus inactivators. Here we have highlighted recent progress in developing PPVIs against several important enveloped viruses, including HIV, influenza virus, Zika virus (ZIKV), dengue virus (DENV), and herpes simplex virus (HSV), and the potential use of PPVIs for urgent treatment of infection by newly emerging or re-emerging viruses.

The COVID-19 pandemic is driving the search for new antiviral techniques. Bacteria and fungi are known to be inactivated not only by ultraviolet radiation but also by visible light. Several studies have recently appeared on this subject, in which viruses were mainly irradiated in media. However, it is an open question to what extent the applied media, and especially their riboflavin concentration, can influence the results. A literature search identified appropriate virus photoinactivation publications and, where possible, viral light susceptibility was quantitatively determined in terms of average log-reduction doses. Sensitivities of enveloped viruses were plotted against assumed riboflavin concentrations. Viruses appear to be sensitive to visible (violet/blue) light. The median log-reduction doses of all virus experiments performed in liquids is 58 J/cm2. For the non-enveloped, enveloped and coronaviruses only, they were 222, 29 and 19 J/cm2, respectively. Data are scarce, but it appears that (among other things) the riboflavin concentration in the medium has an influence on the log-reduction doses. Experiments with DMEM, with its 0.4 mg/L riboflavin, have so far produced results with the greatest viral susceptibilities. It should be critically evaluated whether the currently published virus sensitivities are really only intrinsic properties of the virus, or whether the medium played a significant role. In future experiments, irradiation should be carried out in solutions with the lowest possible riboflavin concentration.

Diphyllin is a natural arylnaphtalide lignan extracted from tropical plants of particular importance in traditional Chinese medicine. This compound has been described as a potent inhibitor of vacuolar (H+)ATPases and hence of the endosomal acidification process that is required by numerous enveloped viruses to trigger their respective viral infection cascades after entering host cells by receptor-mediated endocytosis. Accordingly, we report here a revised, updated, and improved synthesis of diphyllin, and demonstrate its antiviral activities against a panel of enveloped viruses from Flaviviridae, Phenuiviridae, Rhabdoviridae, and Herpesviridae families. Diphyllin is not cytotoxic for Vero and BHK-21 cells up to 100 µM and exerts a sub-micromolar or low-micromolar antiviral activity against tick-borne encephalitis virus, West Nile virus, Zika virus, Rift Valley fever virus, rabies virus, and herpes-simplex virus type 1. Our study shows that diphyllin is a broad-spectrum host cell-targeting antiviral agent that blocks the replication of multiple phylogenetically unrelated enveloped RNA and DNA viruses. In support of this, we also demonstrate that diphyllin is more than just a vacuolar (H+)ATPase inhibitor but may employ other antiviral mechanisms of action to inhibit the replication cycles of those viruses that do not enter host cells by endocytosis followed by low pH-dependent membrane fusion.