MA104 Cell line presents characteristics suitable for enterovirus A71 isolation and proliferation

The internal ribosome entry site determines the neurotropic potential of enterovirus A71

The mechanisms underlying tissue-specific replication of enteroviruses are currently unclear. Although enterovirus A71 (EV-A71) and coxsackievirus A16 (CV-A16) are both common pathogens that cause hand-foot-mouth disease, they display quite different neurotropic properties. Herein, we characterized the role of the internal ribosomal entry site (IRES) in determining neurovirulence using an oral inoculation model of EV-A71. The receptor transgenic (hSCARB2-Tg) mice developed neurological symptoms after being infected with a mouse-adapted EV-A71 strain (MP4) via different administrative routes. Intragastric administration of the MP4 strain caused pathological changes such as neuronal loss and neuropil vacuolation, whereas replacing EV-A71 IRES with CV-A16 abolished the neuropathological phenotypes. The attenuated neurotropic potential of IRES-swapped EV-A71 was observed even in mice that received intraperitoneal and intracerebral inoculations. Fewer chimeric MP4 viral RNAs and proteins were detected in the mouse tissues, regardless of the inoculation route. Tissue-specific replication can be reflected in cell-based characterization. While chimeric MP4 virus replicated poorly in human intestinal C2BBe1 and neuroblastoma SH-SY5Y cells, its replication in susceptible rhabdomyosarcoma cells was not affected. Overall, our results demonstrated that the IRES determined the neurotropic potential of EV-A71 and CV-A16, emphasizing the importance of the IRES in tissue tropism, along with the host receptors.

Molecular Epidemiology of Enterovirus in Children with Central Nervous System Infections

Limited recent molecular epidemiology data are available for pediatric Central Nervous System (CNS) infections in Europe. The aim of this study was to investigate the molecular epidemiology of enterovirus (EV) involved in CNS infections in children. Cerebrospinal fluid (CSF) from children (0–16 years) with suspected meningitis–encephalitis (ME) who were hospitalized in the largest pediatric hospital of Greece from October 2017 to September 2020 was initially tested for 14 common pathogens using the multiplex PCR FilmArray^® ME Panel (FA-ME). CSF samples positive for EV, as well as pharyngeal swabs and stools of the same children, were further genotyped employing Sanger sequencing. Of the 330 children tested with FA-ME, 75 (22.7%) were positive for EV and 50 different CSF samples were available for genotyping. The median age of children with EV CNS infection was 2 months (IQR: 1–60) and 44/75 (58.7%) of them were male. There was a seasonal distribution of EV CNS infections, with most cases detected between June and September (38/75, 50.7%). EV genotyping was successfully processed in 84/104 samples: CSF (n = 45/50), pharyngeal swabs (n = 15/29) and stools (n = 24/25). Predominant EV genotypes were CV-B5 (16/45, 35.6%), E30 (10/45, 22.2%), E16 (6/45, 13.3%) and E11 (5/45, 11.1%). However, significant phylogenetic differences from previous described isolates were detected. No unusual neurologic manifestations were observed, and all children recovered without obvious acute sequelae. Specific EV circulating genotypes are causing a significant number of pediatric CNS infections. Phylogenetic analysis of these predominant genotypes found genetic differences from already described EV isolates.

Characterization of Plaque Variants and the Involvement of Quasi-Species in a Population of EV-A71

Viral plaque morphologies in human cell lines are markers for growth capability and they have been used to assess the viral fitness and selection of attenuated mutants for live-attenuated vaccine development. In this study, we investigate whether the naturally occurring plaque size variation reflects the virulence of the variants of EV-A71. Variants of two different plaque sizes (big and small) from EV-A71 sub-genotype B4 strain 41 were characterized. The plaque variants displayed different in vitro growth kinetics compared to the parental wild type. The plaque variants showed specific mutations being present in each variant strain. The big plaque variants showed four mutations I97L, N104S, S246P and N282D in the VP1 while the small plaque variants showed I97T, N237T and T292A in the VP1. No other mutations were detected in the whole genome of the two variants. The variants showed stable homogenous small plaques and big plaques, respectively, when re-infected in rhabdomyosarcoma (RD) and Vero cells. The parental strain showed faster growth kinetics and had higher viral RNA copy number than both the big and small plaque variants. Homology modelling shows that both plaque variants have differences in the structure of the VP1 protein due to the presence of unique spontaneous mutations found in each plaque variant This study suggests that the EV-A71 sub-genotype B4 strain 41 has at least two variants with different plaque morphologies. These differences were likely due to the presence of spontaneous mutations that are unique to each of the plaque variants. The ability to maintain the respective plaque morphology upon passaging indicates the presence of quasi-species in the parental population.

Virucidal activity and the antiviral mechanism of acidic polysaccharides against Enterovirus 71 infection in vitro

Enterovirus 71 (EV71) is the predominant pathogen for severe hand, foot, and mouth disease (HFMD) in children younger than 5 years, and currently no effective drugs are available for EV71. Thus, there is an urgent need to develop new drugs for the control of EV71 infection. In this study, LJ04 was extracted from Laminaria japonica using diethylaminoethyl cellulose-52 with 0.4 mol/l NaCl as the eluent, and its virucidal activity was evaluated based on its cytopathic effects on a microplate. LJ04 is composed of fucose, galactose, and mannose and mainly showed good virucidal activity against EV71. The antiviral mechanisms of LJ04 were the direct inactivation of the virus, the blockage of virus binding, disruptions to viral entry, and weak inhibitory activity against the nonstructural protein 3C. The two most important findings from this study were that LJ04 inhibited EV71 proliferation in HM1900 cells, which are a human microglia cell line, and that LJ04 can directly inactivate EV71 within 2 hr at 37°C. This study demonstrates for the first time the ability of a polysaccharide from L. japonica to inhibit viral and 3C activity; importantly, the inhibition of 3C might have a minor effect on the antiviral effect of LJ04. Consequently, our results identify LJ04 as a potential drug candidate for the control of severe EV71 infection in clinical settings.

Antiviral activity of a polysaccharide from Laminaria japonica against enterovirus 71

This in vitro study investigated the antiviral activity of an acidic polysaccharide from Laminaria japonica against enterovirus 71 (EV71) as well as its mechanism of action. The LJ04 polysaccharide was purified from Laminaria japonica by affinity chromatography. To investigate its antiviral activity, an MTT assay, q-PCR, immunofluorescent staining and western-blot analysis were performed. To define its mechanism of action, ELISA, q-PCR and flow cytometry were conducted. LJ04 had a low EC50, high CC50 and high SI. LJ04 inhibited not only JN200804, but also JN200803 in RD cells, and viral proliferation was strongly inhibited, whereas LJ04 suppressed viral-induced apoptosis as detected by flow cytometry. In conclusion, LJ04 was found to have robust antiviral activity by inhibiting apoptosis and inducing IFN-β expression. Our findings indicate that LJ04 is a good candidate for the treatment of EV71.

A Novel Enterovirus 71 (EV71) Virulence Determinant: The 69th Residue of 3C Protease Modulates Pathogenicity

Human enterovirus type 71 (EV71), the major causative agent of hand-foot-and-mouth disease, has been known to cause fatal neurological complications. Unfortunately, the reason for neurological complications that have been seen in fatal cases of the disease and the relationship between EV71 virulence and viral genetic sequences remains largely undefined. The 3C protease (3Cpro) of EV71 plays an irreplaceable role in segmenting the precursor polyprotein during viral replication, and intervening with host life activity during viral infection. In this study, for the first time, the 69th residue of 3C protease has been identified as a novel virulence determinant of EV71. The recombinant virus with single point variation, in the 69th of 3Cpro, exhibited obvious decline in replication, and virulence. We further determined the crystal structure of 3C N69D at 1.39 Ǻ resolution and found that conformation of 3C N69D demonstrated significant changes compared with a normal 3C protein, in the substrate-binding site and catalytic active site. Strikingly, one of the switch loops, essential in fixing substrates, adopts an open conformation in the 3C N69D-rupintrivir complex. Consistent with this apparent structural disruption, the catalytic activity of 3C N69D decreased sharply for host derived and viral derived substrates, detected for both in vitro and in vivo. Interestingly, in addition to EV71, Asp69 was also found in 3C proteases of other virus strains, such as CAV16, and was conserved in nearly all C type human rhinovirus. Overall, we identified a natural virulence determinant of 3C protease and revealed the mechanism of attenuated virulence is mediated by N69D substitution. Our data provides new insight into the enzymatic mechanism of a subdued 3C protease and suggests a theoretical basis for virulence determinantion of picornaviridae.

Genome analysis of enterovirus 71 strains differing in mouse pathogenicity

Enterovirus 71 (EV71) is a major causative agent of hand, foot, and mouth disease (HFMD) and is occasionally associated with severe neurological diseases. The investigation of virulence determinants of EV71 is rudimentary. Therefore, it is important to understand the relationship between EV71 virulence and genomic information. In this study, a series of analyses about full-length genomic sequence were performed on six EV71 strains isolated from HFMD patients with either severe or mild clinical symptoms. A one-day-old BALB/c mouse model was used to study the infection characteristics. Results showed all six strains were of the subgenogroup C4a. Viral full-length genomic sequence analysis showed that a total of 40 nucleotide differences between strains of highly and low virulence were revealed. Among all mutations, three nucleotide mutations were found in the untranslated region. A mutation, nt115, at internal ribozyme entry site (IRES) caused RNA secondary structural change. The other 37 mutations were all located in the open reading frame resulting in 8 amino acid mutations. Importantly, we discovered that a mutation of amino acid (Asn1617 → Asp1617) in the 3C proteinase (3C(pro)) of highly and low pathogenic strains could lead to conformational change at the active center, suggesting that this site may be a virulence determinant of EV71.

Comparing in vivo biodistribution with radiolabeling and Franz cell permeation assay to validate the efficacy of both methodologies in the evaluation of nanoemulsions: a safety approach

The Franz cells permeation assay has been performed for over 25 years. However, the advent of nanotechnology created a whole new world, especially with regard to topical products. In this new global scenario an increasing number of nanostructure-based delivery systems (NDSs) have emerged and a global warning relating to the safety of these NDSs is arising. This work studied the efficacy of the Franz cells assay, comparing it with the radiolabeling biodistribution test. For this purpose a formulation of sunscreen based on an NDS was developed and characterized. The results demonstrated both that the NDS did not present in vitro cytotoxicity and that the radiolabeling biodistribution test is more precise for the evaluation of NDS cosmetics than the Franz cells assay, since it detected the permeation of the NDS at a picogram order. Due to this fact, and considering all the concerns related to NDSs and nanoparticles in general, more precise methods must be used in order to guarantee the safe use of these new classes of products.