Potent Inhibition of Hepatitis E Virus Release by a Cyclic Peptide Inhibitor of the Interaction between Viral Open Reading Frame 3 Protein and Host Tumor Susceptibility Gene 101

ESCRT machinery and virus infection

The endosomal sorting complex required for transport (ESCRT) machinery plays a significant role in the spread of human viruses. However, our understanding of how the host ESCRT machinery responds to viral infection remains limited. Emerging evidence suggests that the ESCRT machinery can be hijacked by viruses of different families to enhance their replication. Throughout their life cycle, these viruses can interfere with or exploit ESCRT-mediated physiological processes to increase their chances of infecting the host. In contrast, to counteract virus infection, the interferon-stimulated gene 15 (ISG15) or the E3 ISG15-protein ligase (HERC5) system within the infected cells is activated to degrade the ESCRT proteins. Many retroviral and RNA viral proteins have evolved "late (L) domain" motifs, which enable them to recruit host ESCRT subunit proteins to facilitate virus transport, replication, budding, mature, and even endocytosis, Therefore, the L domain motifs and ESCRT subunit proteins could serve as promising drug targets for antiviral therapy. This review investigated the composition and essential functions of the ESCRT, shedding light on the impact of ESCRT subunits and viral L domain motifs on the replication of viruses. Furthermore, the antiviral effects facilitated by the ESCRT machinery have been investigated, aiming to provide valuable insights to guide the development and utilization of antiviral drugs.

Discovery of non-nucleoside oxindole derivatives as potent inhibitors against dengue RNA-dependent RNA polymerase

A series of thiazole linked Oxindole-5-Sulfonamide (OSA) derivatives were designed as inhibitors of RNA-dependent RNA polymerase (RdRp) activity of Dengue virus. These were synthesized and then evaluated for their efficacy in ex-vivo virus replication assay using human cell lines. Among 20 primary compounds in the series, OSA-15 was identified as a hit. A series of analogues were synthesized by replacing the difluoro benzyl group of OSA-15 with different substituted benzyl groups. The efficacy of OSA-15derivatives was less than that of the parent compound, except OSA-15-17, which has shown improved efficacy than OSA-15. The further optimization was carried out by adding dimethyl (DM) groups to both the sulfonamide and oxindole NH's to produce OSA-15-DM and OSA-15-17-DM. These two compounds were showing no detectable cytotoxicity and the latter was more efficacious. Further, both these compounds were tested for inhibition in all the serotypes of the Dengue virus using an ex-vivo assay. The EC₅₀ of OSA-15-17-DM was observed in a low micromolar range between 2.5 and 5.0 µg/ml. Computation docking and molecular dynamics simulation studies confirmed the binding of identified hits to DENV RdRp. OSA15-17-DM blocks the RNA entrance and elongation site for their biological activity with high binding affinity. Overall, the identified oxindole derivatives are novel compounds that can inhibit Dengue replication, working as non-nucleoside inhibitors (NNI) to explore as anti-viral RdRp activity.

A Review: The Antiviral Activity of Cyclic Peptides

In the design and development of therapeutic agents, macromolecules with restricted structures have stronger competitive edges than linear biological entities since cyclization can overcome the limitations of linear structures. The common issues of linear peptides include susceptibility to degradation of the peptidase enzyme, off-target effects, and necessity of routine dosing, leading to instability and ineffectiveness. The unique conformational constraint of cyclic peptides provides a larger surface area to interact with the target at the same time, improving the membrane permeability and in vivo stability compared to their linear counterparts. Currently, cyclic peptides have been reported to possess various activities, such as antifungal, antiviral and antimicrobial activities. To date, there is emerging interest in cyclic peptide therapeutics, and increasing numbers of clinically approved cyclic peptide drugs are available on the market. In this review, the medical significance of cyclic peptides in the defence against viral infections will be highlighted. Except for chikungunya virus, which lacks specific antiviral treatment, all the viral diseases targeted in this review are those with effective treatments yet with certain limitations to date. Thus, strategies and approaches to optimise the antiviral effect of cyclic peptides will be discussed along with their respective outcomes. Apart from isolated naturally occurring cyclic peptides, chemically synthesized or modified cyclic peptides with antiviral activities targeting coronavirus, herpes simplex viruses, human immunodeficiency virus, Ebola virus, influenza virus, dengue virus, five main hepatitis viruses, termed as type A, B, C, D and E and chikungunya virus will be reviewed herein.

Graphical Abstract

Structure-based virtual screening, molecular dynamics simulation and in vitro evaluation to identify inhibitors against NAMPT

Nicotinamide phosphoribosyltransferase (NAMPT) is a bottleneck enzyme that plays a key role in recycling nicotinamide to maintain the adequate NAD + level inside the cell. It involves maintaining the cellular bioenergetics and providing a necessary substrate for functions essential to rapidly proliferating the cancer cells. Therefore, inhibition of NAMPT appears as a therapeutic potential for cancer treatment. Here, the vast virtual screening followed by focused docking and in-vitro analysis was carried out to identify the promising hits of NAMPT. We have identified two potential hits from the filtered molecules, which are chemically diverse and have shown comparable quantitative values with reported co-crystal '1QS' as their binding pattern matched nicely. These two compounds are further explored through molecular dynamics simulations (MD) combined with pharmacokinetics profiling and thermodynamic analysis demonstrating their suitability as novel NAMPT inhibitors that can be used as starting points for a hit-to-lead campaign.Communicated by Ramaswamy H. Sarma.

Characterizing (un)binding mechanism of USP7 inhibitors to unravel the cause of enhanced binding potencies at allosteric checkpoint

The ability to predict the intricate mechanistic behavior of ligands and associated structural determinants during protein-ligand (un)binding is of great practical importance in drug discovery. Ubiquitin specific protease-7 (USP7) is a newly emerging attractive cancer therapeutic target with bound allosteric inhibitors. However, none of the inhibitors have reached clinical trials, allowing opportunities to examine every aspect of allosteric modulation. The crystallographic insights reveal that these inhibitors have common properties such as chemical scaffolds, binding site and interaction fingerprinting. However, they still possess a broader range of binding potencies, ranging from 22 nM to 1,300 nM. Hence, it becomes more critical to decipher the structural determinants guiding the enhanced binding potency of the inhibitors. In this regard, we elucidated the atomic-level insights from both interacting partners, that is, protein-ligand perspective, and established the structure-activity link between USP7 inhibitors by using classical and advanced molecular dynamics simulations combined with linear interaction energy and molecular mechanics-Poisson Boltzmann surface area. We revealed the inhibitor potency differences by examining the contributions of chemical moieties and USP7 residues, the involvement of water-mediated interactions, and the thermodynamic landscape alterations. Additionally, the dissociation profiles aided in the establishment of a correlation between experimental potencies and structural determinants. Our study demonstrates the critical role of blocking loop 1 in allosteric inhibition and enhanced binding affinity. Comprehensively, our findings provide a constructive expansion of experimental outcomes and show the basis for varying binding potency using in-silico approaches. We expect this atomistic approach to be useful for effective drug design.

Prospecting for Cressa cretica to treat COVID-19 via in silico molecular docking models of the SARS-CoV-2

The severe acute respiratory syndrome COVID-19 declared as a global pandemic by the World Health Organization has become the present wellbeing worry to the whole world. There is an emergent need to search for possible medications. Cressa cretica is reported to show antitubercular, antibacterial and expectorant property. In this research, we aim to prospect the COVID-19 main protease crystal structure (Mpro; PDB ID: 6LU7) and the active chemical constituents from Cressa cretica in order to understand the structural basis of their interactions. We examined the binding potential of active constituents of Cressa cretica plant to immensely conserved protein Mpro of SARS-CoV-2 followed by exploration of the vast conformational space of protein-ligand complexes by molecular dynamics (MD) simulations. The results suggest the effectiveness of 3,5-Dicaffeoylquinic acid and Quercetin against standard drug Remdesivir. The active chemical constituents exhibited good docking scores, and interacts with binding site residues of Mpro by forming hydrogen bond and hydrophobic interactions. 3,5-Dicaffeoylquinic acid showed the best affinity towards Mpro receptor which is one of the target enzymes required by SARS CoV-2 virus for replication suggesting it to be a novel research molecule. The potential of the active chemical constituents from Cressa cretica against the SARS-CoV-2 virus has best been highlighted through this study. Therefore, these chemical entities can be further scrutinized and provides direction for further consideration for in-vivo and in-vitro validations for the treatment of covid-19. Communicated by Ramaswamy H. Sarma.

Antimicrobial peptides and their potential application in antiviral coating agents

Coronavirus pandemic has evidenced the importance of creating bioactive materials to mitigate viral infections, especially in healthcare settings and public places. Advances in antiviral coatings have led to materials with impressive antiviral performance; however, their application may face health and environmental challenges. Bio-inspired antimicrobial peptides (AMPs) are suitable building blocks for antimicrobial coatings due to their versatile design, scalability, and environmentally friendly features. This review presents the advances and opportunities on the AMPs to create virucidal coatings. The review first describes the fundamental characteristics of peptide structure and synthesis, highlighting the recent findings on AMPs and the role of peptide structure (α-helix, β-sheet, random, and cyclic peptides) on the virucidal mechanism. The following section presents the advances in AMPs coating on medical devices with a detailed description of the materials coated and the targeted pathogens. The use of peptides in vaccine formulations is also reported, emphasizing the molecular interaction of peptides with different viruses and the current clinical stage of each formulation. The role of several materials (metallic particles, inorganic materials, and synthetic polymers) in the design of antiviral coatings is also presented, discussing the advantages and the drawbacks of each material. The final section offers future directions and opportunities for using AMPs on antiviral coatings to prevent viral outbreaks.

Dispersion of synonymous codon usage patterns in hepatitis E virus genomes derived from various hosts

Hepatitis E virus (HEV) is an important zoonotic pathogen infecting a wide range of host species. It has a positive-sense, single-stranded RNA genome encoding three open reading frames (ORFs). Synonymous codon usages of viruses essentially determine their survival and adaptation to susceptible hosts. To better understand the interplay between the ever-expanding host range and synonymous codon usages of HEV, we quantified the dispersion of synonymous codon usages of HEV genomes isolated from different hosts via V_s calculation and information entropy. HEV ORFs show species-specific synonymous codon usage patterns. Ruminant-derived HEV ORFs own the most synonymous codons with stable usage patterns (V_s value <0.1) which leads to the stable overall codon usage patterns (R value being close to zero). Swine-derived HEV ORFs own more concentrated synonymous codons than those from wild boar. Compared with HEV strains isolated from other hosts, the human-derived HEV exhibits a distinct pattern at the overall codon usage (R < 0). Generally, ORF1 contains more synonymous codons with stable usage patterns (V_s  < 0.1) than those of ORFs 2 and 3. Moreover, ORF3 contains more synonymous codons with varied patterns (V_s  > 1.0) than ORFs 1 and 2. The host factor serving as one of the evolutionary dynamics probably influences synonymous codon usage patterns of the HEV genome. Taken together, synonymous codons with stable usage patterns in ORF1 might help to sustain the infection, while that with varied usage patterns in ORF3 may facilitate cross-species infection and expand the host range.

Antiviral Activity of Zinc Oxide Nanoparticles and Tetrapods Against the Hepatitis E and Hepatitis C Viruses

Hepatitis E virus (HEV) causes an acute, self-limiting hepatitis. The disease takes a severe form in pregnant women, leading to around 30% mortality. Zinc is an essential micronutrient that plays a crucial role in multiple cellular processes. Our earlier findings demonstrated the antiviral activity of zinc salts against HEV infection. Zinc oxide (ZnO) and its nanostructures have attracted marked interest due to their unique characteristics. Here we synthesized ZnO nanoparticles [ZnO(NP)] and tetrapod-shaped ZnO nanoparticles [ZnO(TP)] and evaluated their antiviral activity. Both ZnO(NP) and ZnO(TP) displayed potent antiviral activity against hepatitis E and hepatitis C viruses, with the latter being more effective. Measurement of cell viability and intracellular reactive oxygen species levels revealed that both ZnO(NP) and ZnO(TP) are noncytotoxic to the cells even at significantly higher doses, compared to a conventional zinc salt (ZnSO₄). Our study paves the way for evaluation of the potential therapeutic benefit of ZnO(TP) against HEV and HCV.

Understanding binding affinity and specificity of modular protein domains: A focus in ligand design for the polyproline-binding families

Within the modular protein domains there are five families that recognize proline-rich sequences: SH3, WW, EVH1, GYF and UEV domains. This chapter reviews the main strategies developed for the design of ligands for these families, including peptides, peptidomimetics and drugs. We also describe some studies aimed to understand the molecular reasons responsible for the intrinsic affinity and specificity of these domains.

Mandal S, Choudhury SM. Short Amphiphiles or Micelle Peptides May Help to Fight Against COVID-19

Background:

COVID-19 is a worldwide threat because of the incessant spread of SARS-CoV-2 which urges the development of suitable antiviral drug to secure our society. Already, a group of peptides have been recommended for SARS-CoV-2, but not yet established. SARS-CoV-2 is an enveloped virus with hydrophobic fusion protein and spike glycoproteins.

Methods:

Here, we have summarized several reported amphiphilic peptides and their in-silico docking analysis with spike glycoprotein of SARS-CoV-2.

Result:

The result revealed the complex formation of spike protein and amphiphilic peptides with higher binding affinity. It was also observed that PalL1 (ARLPRTMVHPKPAQP), 10AN1 (FWFTLIKTQAKQPARYRRFC), THETA defensin (RCICGRGICRLL) and mucroporin M1 (LFRLIKSLIKRLVSAFK) showed the binding free energy more than -1000 kcal/mol. Molecular pI and hydrophobicity are also important factors of peptides to enhance the binding affinity with spike protein of SARS-CoV-2

Conclusion:

In the light of these findings, it is necessary to check the real efficacy of amphiphilic peptides in-vitro to in-vivo experimental set up to develop an effective anti-SARS-CoV-2 peptide drug, which might help to control the current pandemic situation.

Conformational Characterization of the Co-Activator Binding Site Revealed the Mechanism to Achieve the Bioactive State of FXR

FXR bioactive states are responsible for the regulation of metabolic pathways, which are modulated by agonists and co-activators. The synergy between agonist binding and ‘co-activator’ recruitment is highly conformationally driven. The characterization of conformational dynamics is essential for mechanistic and therapeutic understanding. To shed light on the conformational ensembles, dynamics, and structural determinants that govern the activation process of FXR, molecular dynamic (MD) simulation is employed. Atomic insights into the ligand binding domain (LBD) of FXR revealed significant differences in inter/intra molecular bonding patterns, leading to structural anomalies in different systems of FXR. The sole presence of an agonist or ‘co-activator’ fails to achieve the essential bioactive conformation of FXR. However, the presence of both establishes the bioactive conformation of FXR as they modulate the internal wiring of key residues that coordinate allosteric structural transitions and their activity. We provide a precise description of critical residue positioning during conformational changes that elucidate the synergy between its binding partners to achieve an FXR activation state. Our study offers insights into the associated modulation occurring in FXR at bound and unbound forms. Thereafter, we also identified hot-spots that are critical to arrest the activation mechanism of FXR that would be helpful for the rational design of its agonists.

Molecular Dynamics Simulations Reveal the Interaction Fingerprint of Remdesivir Triphosphate Pivotal in Allosteric Regulation of SARS-CoV-2 RdRp

The COVID-19 pandemic has now strengthened its hold on human health and coronavirus' lethal existence does not seem to be going away soon. In this regard, the optimization of reported information for understanding the mechanistic insights that facilitate the discovery towards new therapeutics is an unmet need. Remdesivir (RDV) is established to inhibit RNA-dependent RNA polymerase (RdRp) in distinct viral families including Ebola and SARS-CoV-2. Therefore, its derivatives have the potential to become a broad-spectrum antiviral agent effective against many other RNA viruses. In this study, we performed comparative analysis of RDV, RMP (RDV monophosphate), and RTP (RDV triphosphate) to undermine the inhibition mechanism caused by RTP as it is a metabolically active form of RDV. The MD results indicated that RTP rearranges itself from its initial RMP-pose at the catalytic site towards NTP entry site, however, RMP stays at the catalytic site. The thermodynamic profiling and free-energy analysis revealed that a stable pose of RTP at NTP entrance site seems critical to modulate the inhibition as its binding strength improved more than its initial RMP-pose obtained from docking at the catalytic site. We found that RTP not only occupies the residues K545, R553, and R555, essential to escorting NTP towards the catalytic site, but also interacts with other residues D618, P620, K621, R624, K798, and R836 that contribute significantly to its stability. From the interaction fingerprinting it is revealed that the RTP interact with basic and conserved residues that are detrimental for the RdRp activity, therefore it possibly perturbed the catalytic site and blocked the NTP entrance site considerably. Overall, we are highlighting the RTP binding pose and key residues that render the SARS-CoV-2 RdRp inactive, paving crucial insights towards the discovery of potent inhibitors.

Hepatitis E virus egress and beyond - the manifold roles of the viral ORF3 protein

Although the hepatitis E virus represents an uprising threat to the global community by representing the commonest cause of an acute viral hepatitis worldwide, its life cycle is grossly understudied. Albeit HEV is a non-enveloped virus, its progeny is released as quasi-enveloped virions. Thus, the responsible accessory protein pORF3 gained rising attention in the past years. It mediates viral release via the exosomal route by targeting the viral capsid to the endosomal system, more precisely to multivesicular bodies. As this is followed by quasi-envelopment, pORF3 may in terms represent a substitute to a conventional envelope protein. This feature proofs to be rather unique with respect to other enteric viruses, although the protein's role in the viral life cycle seems to reach far beyond simply maintaining release of progeny viruses. How pORF3 affects viral morphogenesis, how it mediates efficient viral release and how it supports viral spread is summarised in this microreview. With this, we aim to shed light on functions of pORF3 to gain further insights in still enigmatic aspects of the HEV life cycle. TAKE AWAYS: HEV is released as exosome via multivesicular bodies Viral pORF3 mediates release via endosomal complexes required for transport pORF3 modulates various cellular processes in infected cells Elucidation of pORF3-related processes imply novel clinical strategies.

Identification of potential molecules against COVID-19 main protease through structure-guided virtual screening approach

The pandemic caused by novel coronavirus disease 2019 (COVID-19) infecting millions of populations worldwide and counting, has demanded quick and potential therapeutic strategies. Current approved drugs or molecules under clinical trials can be a good pool for repurposing through in-silico techniques to quickly identify promising drug candidates. The structural information of recently released crystal structures of main protease (Mpro) in APO and complex with inhibitors, N3, and 13b molecules was utilized to explore the binding site architecture through Molecular dynamics (MD) simulations. The stable state of Mpro was used to conduct extensive virtual screening of the aforementioned drug pool. Considering the recent success of HIV protease molecules, we also used anti-protease molecules for drug repurposing purposes. The identified top hits were further evaluated through MD simulations followed by the binding free energy calculations using MM-GBSA. Interestingly, in our screening, several promising drugs stand out as potential inhibitors of Mpro. However, based on control (N3 and 13b), we have identified six potential molecules, Leupeptin Hemisulphate, Pepstatin A, Nelfinavir, Birinapant, Lypression and Octreotide which have shown the reasonably significant MM-GBSA score. Further insight shows that the molecules form stable interactions with hot-spot residues, that are mainly conserved and can be targeted for structure- and pharmacophore-based designing. The pharmacokinetic annotations and therapeutic importance have suggested that these molecules possess drug-like properties and pave their way for in-vitro studies.Communicated by Ramaswamy H. Sarma.

Binding mode characterization of 13b in the monomeric and dimeric states of SARS-CoV-2 main protease using molecular dynamics simulations

The main protease, M^pro/3CL^pro, plays an essential role in processing polyproteins translated from viral RNA to produce functional viral proteins and therefore serve as an attractive target for discovering COVID-19 therapeutics. The availability of both monomer and dimer crystal bound with a common ligand, '13b' (α-ketoamide inhibitor), opened up opportunities to understand the M^pro mechanism of action. A comparative analysis of both forms of M^pro was carried out to elucidate the binding site architectural differences in the presence and absence of '13b'. Molecular dynamics simulations suggest that the presence of '13b' enhances the stability of M^pro than the unbound APO form. The N- and C- terminals of both the protomers stabilize each other, and making it's interface essential for the active form of M^pro. In comparison to monomer, the relatively high affinity of '13b' is gained in dimer pocket due to the high stability of the pocket by the interaction of S1 residue of chain B with residues F140, E166 and H172 of chain A, which is absent in monomer. The comprehensive essential dynamics, protein structure network analysis and thermodynamic profiling highlight the hot-spots, pivotal in molecular recognition process at protein-ligand and protein-protein interaction levels, cross-validated through computational alanine scanning study. A comparative description of '13b' binding mechanism in both forms illustrates valuable insights into the inhibition mechanism and the selection of critical residues suitable for the structure-based approaches for the identification of more potent M^pro inhibitors.Communicated by Ramaswamy H. Sarma.

Protein Interaction Domains: Structural Features and Drug Discovery Applications (Part 2)

BACKGROUND

Proteins present a modular organization made up of several domains. Apart from the domains playing catalytic functions, many others are crucial to recruit interactors. The latter domains can be defined as "PIDs" (Protein Interaction Domains) and are responsible for pivotal outcomes in signal transduction and a certain array of normal physiological and disease-related pathways. Targeting such PIDs with small molecules and peptides able to modulate their interaction networks, may represent a valuable route to discover novel therapeutics.

OBJECTIVE

This work represents a continuation of a very recent review describing PIDs able to recognize post-translationally modified peptide segments. On the contrary, the second part concerns with PIDs that interact with simple peptide sequences provided with standard amino acids.

METHODS

Crucial structural information on different domain subfamilies and their interactomes was gained by a wide search in different online available databases (including the PDB (Protein Data Bank), the Pfam (Protein family), and the SMART (Simple Modular Architecture Research Tool)). Pubmed was also searched to explore the most recent literature related to the topic.

RESULTS AND CONCLUSION

PIDs are multifaceted: they have all diverse structural features and can recognize several consensus sequences. PIDs can be linked to different diseases onset and progression, like cancer or viral infections and find applications in the personalized medicine field. Many efforts have been centered on peptide/peptidomimetic inhibitors of PIDs mediated interactions but much more work needs to be conducted to improve drug-likeness and interaction affinities of identified compounds.

Screening and Molecular Modeling Evaluation of Food Peptides to Inhibit Key Targets of COVID-19 Virus

Peptide drugs, especially food-derived peptides, have a variety of functional activities including antiviral and may also have a therapeutic effect on COVID-19. In this study, comparing with the reported drugs, 79 peptides were found to bind to the key targets of COVID-19 virus with higher non-covalent interaction, while among them, six peptides showed high non-covalent interactions with the three targets, which may inhibit the COVID-19 virus. In the simulation, peptides of nine to 10 amino acids with a hydrophilic amino acid and acidic amino acid in the middle and aromatic amino acids on the side showed higher binding to angiotensin-converting enzyme 2 (ACE2). Peptides of five to six amino acids with a basic amnio acid in the head, acidic amnio acid in the neck, hydrophobicity group in the middle, and basic amino acids in the tail showed higher binding to COVID-19 virus main protease (Mpro), while those with basic amino acids and acidic amino acids in the two sides and aromatic amino acids in the middle might have stronger interaction with COVID-19 virus RNA-dependent RNA polymerase (RdRp).

Japanese encephalitis virus capsid protein interacts with non-lipidated MAP1LC3 on replication membranes and lipid droplets

Microtubule-associated protein 1 light chain 3 (MAP1LC3) is a protein with a well-defined function in autophagy, but still incompletely understood roles in several other autophagy-independent processess. Studies have shown MAP1LC3 is a host-dependency factor for the replication of several viruses. Japanese encephalitis virus (JEV), a neurotropic flavivirus, replicates on ER-derived membranes that are marked by autophagosome-negative non-lipidated MAP1LC3 (LC3-I). Depletion of LC3 exerts a profound inhibition on virus replication and egress. Here, we further characterize the role of LC3 in JEV replication, and through immunofluorescence and immunoprecipitation show that LC3-I interacts with the virus capsid protein in infected cells. This association was observed on capsid localized to both the replication complex and lipid droplets (LDs). JEV infection decreased the number of LDs per cell indicating a link between lipid metabolism and virus replication. This capsid-LC3 interaction was independent of the autophagy adaptor protein p62/Sequestosome 1 (SQSTM1). Further, no association of capsid was seen with the Gamma-aminobutyric acid receptor-associated protein family, suggesting that this interaction was specific for LC3. High-resolution protein-protein docking studies identified a putative LC3-interacting region in capsid, 56FTAL59, and other key residues that could mediate a direct interaction between the two proteins.

Hepatitis E Virus Infection: Circulation, Molecular Epidemiology, and Impact on Global Health

Infection with hepatitis E virus (HEV) represents the most common source of viral hepatitis globally. Although infecting over 20 million people annually in endemic regions, with major outbreaks described since the 1950s, hepatitis E remains an underestimated disease. This review gives a current view of the global circulation and epidemiology of this emerging virus. The history of HEV, from the first reported enteric non-A non-B hepatitis outbreaks, to the discovery of the viral agent and the molecular characterization of the different human pathogenic genotypes, is discussed. Furthermore, the current state of research regarding the virology of HEV is critically assessed, and the challenges towards prevention and diagnosis, as well as clinical risks of the disease described. Together, these points aim to underline the significant impact of hepatitis E on global health and the need for further in-depth research to better understand the pathophysiology and its role in the complex disease manifestations of HEV infection.

Intercellular Transmission of Naked Viruses through Extracellular Vesicles: Focus on Polyomaviruses

Extracellular vesicles have recently emerged as a novel mode of viral transmission exploited by naked viruses to exit host cells through a nonlytic pathway. Extracellular vesicles can allow multiple viral particles to collectively traffic in and out of cells, thus enhancing the viral fitness and diversifying the transmission routes while evading the immune system. This has been shown for several RNA viruses that belong to the Picornaviridae, Hepeviridae, Reoviridae, and Caliciviridae families; however, recent studies also demonstrated that the BK and JC viruses, two DNA viruses that belong to the Polyomaviridae family, use a similar strategy. In this review, we provide an update on recent advances in understanding the mechanisms used by naked viruses to hijack extracellular vesicles, and we discuss the implications for the biology of polyomaviruses.

BK Polyomavirus Hijacks Extracellular Vesicles for En Bloc Transmission

Reactivation of BKPyV is responsible for nephropathies in kidney transplant recipients, which frequently lead to graft loss. The mechanisms of persistence and immune evasion used by this virus remain poorly understood, and a therapeutic option for transplant patients is still lacking. Here, we show that BKPyV can be released into EVs, enabling viral particles to infect cells using an alternative entry pathway. This provides a new view of BKPyV pathogenesis. Even though we did not find any decreased sensitivity to neutralizing antibodies when comparing EV-associated particles and naked virions, our study also raises important questions about developing prevention strategies based on the induction or administration of neutralizing antibodies. Deciphering this new release pathway could enable the identification of therapeutic targets to prevent BKPyV nephropathies. It could also lead to a better understanding of the pathophysiology of other polyomaviruses that are associated with human diseases.

Most people are asymptomatic carriers of the BK polyomavirus (BKPyV), but the mechanisms of persistence and immune evasion remain poorly understood. Furthermore, BKPyV is responsible for nephropathies in kidney transplant recipients. Unfortunately, the sole therapeutic option is to modulate immunosuppression, which increases the risk of transplant rejection. Using iodixanol density gradients, we observed that Vero and renal proximal tubular epithelial infected cells release two populations of infectious particles, one of which cosediments with extracellular vesicles (EVs). Electron microscopy confirmed that a single vesicle could traffic tens of viral particles. In contrast to naked virions, the EV-associated particles (eBKPyVs) were not able to agglutinate red blood cells and did not use cell surface sialylated glycans as an attachment factor, demonstrating that different entry pathways were involved for each type of infectious particle. However, we also observed that naked BKPyV and eBKPyV were equally sensitive to neutralization by the serum of a seropositive patient or commercially available polyvalent immunoglobulin preparations, which occurred at a postattachment step, after endocytosis. In conclusion, our work shows a new mechanism that likely plays a critical role during the primary infection and in the persistence, but also the reactivation, of BKPyV.

IMPORTANCE Reactivation of BKPyV is responsible for nephropathies in kidney transplant recipients, which frequently lead to graft loss. The mechanisms of persistence and immune evasion used by this virus remain poorly understood, and a therapeutic option for transplant patients is still lacking. Here, we show that BKPyV can be released into EVs, enabling viral particles to infect cells using an alternative entry pathway. This provides a new view of BKPyV pathogenesis. Even though we did not find any decreased sensitivity to neutralizing antibodies when comparing EV-associated particles and naked virions, our study also raises important questions about developing prevention strategies based on the induction or administration of neutralizing antibodies. Deciphering this new release pathway could enable the identification of therapeutic targets to prevent BKPyV nephropathies. It could also lead to a better understanding of the pathophysiology of other polyomaviruses that are associated with human diseases.

Hepatitis E Virus Drug Development

Hepatitis E virus (HEV) is an underestimated disease, leading to estimated 20 million infections and up to 70,000 deaths annually. Infections are mostly asymptomatic but can reach mortality rates up to 25% in pregnant women or become chronic in immunocompromised patients. The current therapy options are limited to the unspecific antivirals Ribavirin (RBV) and pegylated Interferon-α (pegIFN-α). RBV leads to viral clearance in only 80% of patients treated, and is, similar to pegIFN-α, contraindicated in the major risk group of pregnant women, emphasizing the importance of new therapy options. In this review, we focus on the urgent need and current efforts in HEV drug development. We provide an overview of the current status of HEV antiviral research. Furthermore, we discuss strategies for drug development and the limitations of the approaches with respect to HEV.

Spicatoside A derived from Liriope platyphylla root ethanol extract inhibits hepatitis E virus genotype 3 replication in vitro

Hepatitis E virus (HEV) is the causative agent of hepatitis E in humans worldwide. Although hepatitis E is self-limiting without chronic infection development, HEV infection often leads to severe liver diseases causing high mortality in pregnant women in addition to chronic hepatitis and cirrhosis in immunosuppressed patients. In this study, we investigated the effect of a Liriope platyphylla ethanol extract (LPE) on HEV replication. Interestingly, LPE suppressed replication of the genotype 3 HEV replicon. Sequential solvent fractionation revealed that the ethyl acetate (EA) fraction of LPE exerts the most potent inhibitory effects. With the aid of activity-guided fractionation and multi-step column chromatography, spicatoside A was subsequently isolated in the EA fraction of LPE and specifically shown to exert inhibitory effects on replication of the genotype 3 HEV replicon. In addition, spicatoside A interfered with replication of the HEV genotype 3 strain 47832c and expression of HEV ORF2 capsid proteins. Our findings clearly support the potential utility of spicatoside A as an effective anti-HEV agent.

Life cycle and morphogenesis of the hepatitis E virus

Hepatitis E virus (HEV) is transmitted primarily via contaminated water and food by the fecal oral route and causes epidemics in developing countries. In industrialized countries, zoonotic transmission of HEV is prevalent. In addition, HEV is the major cause of acute hepatitis in healthy adults and can cause chronic hepatitis in immunocompromised patients, with pregnant HEV-infected women having increased mortality rates of approximately 25%. HEV was once an understudied and neglected virus. However, in recent years, the safety of blood products with respect to HEV has increasingly been considered to be a public health problem. The establishment of HEV infection models has enabled significant progress to be made in understanding its life cycle. HEV infects cells via a receptor (complex) that has yet to be identified. The HEV replication cycle is initiated immediately after the (+) stranded RNA genome is released into the cell cytosol. Subsequently, infectious viral particles are released by the ESCRT complex as quasi-enveloped viruses (eHEVs) into the serum, whereas feces and urine contain only nonenveloped infectious viral progeny. The uncoating of the viral envelope takes place in the biliary tract, resulting in the generation of a nonenveloped virus that is more resistant to environmental stress and possesses a higher infectivity than that of eHEV. This review summarizes the current knowledge regarding the HEV life cycle, viral morphogenesis, established model systems and vaccine development.