Inhibition of Orbivirus Replication by Fluvastatin and Identification of the Key Elements of the Mevalonate Pathway Involved

Lipid-targeting antiviral strategies: Current state and future perspectives

There is an urgent need for antiviral compounds effective against currently known and future viral threats. The development of host-targeting antivirals (HTAs) appears as an alternative strategy to fight viral infections minimizing the potential of resistant mutant development and potentially leading to the identification of broad-spectrum antiviral agents. Among the host factors explored for HTA strategy, lipids constitute an attractive target as many viruses, even genetically diverse, hijack specific lipids during their lifecycle. Multiple repurposing efforts have been performed to analyze the antiviral properties of lipid-targeting compounds. These studies include the analysis of the effects of cholesterol lowering drugs such as statins, cholesterol transport inhibitors, sphingolipid modulators, de novo lipogenesis inhibitors blocking fatty acid synthesis, compounds targeting glycerophospholipids or drugs interfering with lipid droplet metabolism. This review is focused on the current status of lipid-based or lipid-targeting antiviral strategies and their potential for the development of antiviral therapies, with special emphasis on those studies that have reached advanced stages of development such as efficacy studies in animal models or clinical trials. Whereas there is still a long way to go, multiple proof-of-concept studies and clinical evidence reinforce the therapeutic potential of these strategies warranting their further development into effective antiviral therapies.

Do Statins Affect Viral Infections Encountered by International Travelers?

Statins are among the most frequently prescribed medications. In addition to their well-established effectiveness in lowering total cholesterol, LDL, and triglycerides, statins have been described to have immunomodulatory and anti-inflammatory properties and have been associated with improved endothelial functions. Given the common use of statins, we sought to evaluate the effect of statins on some viral infections encountered by residents in tropical areas or by international travelers. A literature search was performed in PubMED/MEDLINE focusing on keywords that included statins and the viruses of interest, including SARS-CoV-2, influenza, yellow fever, dengue, Zika, tick-borne encephalitis, hemorrhagic fever viruses, hepatitis A, norovirus, hepatitis B, hepatitis C, measles, and herpesviruses; findings were synthesized for each virus into a summary. The effects of statins on viral infections vary depending on the specific virus. While some studies indicate potential benefits in chronic HBV and HCV infections, evidence regarding SARS-CoV-2 and influenza remains inconclusive due to mixed findings from observational studies and randomized controlled trials. The role of statins in other viral infections is largely unexplored, with preclinical data available for only a few viruses. Given the conflicting evidence, further prospective studies and randomized controlled trials are warranted to elucidate statins' role in viral infections, particularly in modulating inflammation, endothelial dysfunction, and immune responses. Future research should aim to define the optimal patient populations, target viruses, statin types, and treatment durations that may confer benefits in specific viral infections.

Cytokine mRNA Expression Profile in Target Organs of IFNAR (-/-) Mice Infected with African Horse Sickness Virus

African horse sickness (AHS) is a highly severe disease caused by a viral etiological agent, African horse sickness virus (AHSV). It is endemic in sub-Saharan Africa, while sporadic outbreaks have occurred in North Africa, Asia, and Europe, with the most recent cases in Thailand. AHSV transmission between equines occurs primarily by biting midges of the genus Culicoides, especially C. imicola, with a wide distribution globally. As research in horses is highly restricted due to a variety of factors, small laboratory animal models that reproduce clinical signs and pathology observed in natural infection of AHSV are highly needed. Here, we investigated the expression profile of several pro-inflammatory cytokines in target organs and serum of IFNAR (-/-) mice, to continue characterizing this established animal model and to go deep into the innate immune responses that are still needed.

Orbivirus NS4 Proteins Play Multiple Roles to Dampen Cellular Responses

Non-structural protein 4 (NS4) of insect-borne and tick-borne orbiviruses is encoded by genome segment 9, from a secondary open reading frame. Though a protein dispensable for bluetongue virus (BTV) replication, it has been shown to counter the interferon response in cells infected with BTV or African horse sickness virus. We further explored the functional role(s) of NS4 proteins of BTV and the tick-borne Great Island virus (GIV). We show that NS4 of BTV or GIV helps an E3L deletion mutant of vaccinia virus to replicate efficiently in interferon-treated cells, further confirming the role of NS4 as an interferon antagonist. Our results indicate that ectopically expressed NS4 of BTV localised with caspase 3 within the nucleus and was found in a protein complex with active caspase 3 in a pull-down assay. Previous studies have shown that pro-apoptotic caspases (including caspase 3) suppress type I interferon response by cleaving mediators involved in interferon signalling. Our data suggest that orbivirus NS4 plays a role in modulating the apoptotic process and/or regulating the interferon response in mammalian cells, thus acting as a virulence factor in pathogenesis.

Increased Clinical Signs and Mortality in IFNAR(-/-) Mice Immunised with the Bluetongue Virus Outer-Capsid Proteins VP2 or VP5, after Challenge with an Attenuated Heterologous Serotype

Bluetongue is an economically important disease of domesticated and wild ruminants caused by bluetongue virus (BTV). There are at least 36 different serotypes of BTV (the identity of which is determined by its outer-capsid protein VP2), most of which are transmitted by Culicoides biting midges. IFNAR^(-/-) mice immunised with plant-expressed outer-capsid protein VP2 (rVP2) of BTV serotypes -1, -4 or -8, or the smaller outer-capsid protein rVP5 of BTV-10, or mock-immunised with PBS, were subsequently challenged with virulent strains of BTV-4 or BTV-8, or with an attenuated clone of BTV-1 (BTV-1RG_C7). The mice that had received rVP2 generated a protective immune response against the homologous BTV serotype, reducing viraemia (as detected by qRT-PCR), the severity of clinical signs and mortality levels. No cross-serotype protection was observed after challenge with the heterologous BTV serotypes. However, the severity of clinical signs, viraemia and fatality levels after challenge with the attenuated strain of BTV-1 were all increased in mice immunised with rVP2 of BTV-4 and BTV-8, or with rVP5 of BTV10. The possibility is discussed that non-neutralising antibodies, reflecting serological relationships between the outer-capsid proteins of these different BTV serotypes, could lead to 'antibody-dependent enhancement of infection' (ADE). Such interactions could affect the epidemiology and emergence of different BTV strains in the field and would therefore be relevant to the design and implementation of vaccination campaigns.

Establishment of Vero cell lines persistently harboring a yellow fever virus 17D subgenomic replicon

Yellow fever virus (YFV), a member of the genus Flavivirus, family Flaviviridae, is the etiological agent for an acute viral hemorrhagic disease, yellow fever. Although effective live attenuated vaccines based on the strain YFV 17D are currently available, no specific antiviral drug is available, and the disease remains a major public health concern. Hence, the discovery and development of antiviral drugs should lead to great benefits in controlling the disease. To provide a screening platform for antiviral agents targeting YFV RNA translation/replication, we have established and characterized two Vero cell lines that persistently harbor a subgenomic replicon derived from YFV 17D-204 (referred to as replicon cells). The replicon carries YFV nucleotides (1 - 176 and 2382-10,862) and a green fluorescent protein (GFP)-Zeocin resistance fusion gene as a selection marker and indicator of persistent replication. Immunofluorescence analysis revealed that both replicon cells and YFV 17D-infected cells showed similar distribution patterns of viral NS4B protein and replication intermediate, double-stranded RNA. Sequencing analysis of persistent replicons from the two replicon cell lines suggested that their nucleotide sequences did not vary greatly following multiple passages. We examined the effect of five agents, the antiviral cytokines interferon-β and -γ, the nucleoside analog ribavirin, the squalene synthase inhibitor zaragozic acid A, and the antibiotic rifapentine, a recently reported entry and replication inhibitor against YFV, on the persistent replication in the two replicon cell lines. These agents were selected because they inhibited both production of YFV 17D and transient replication of a luciferase-expressing replicon in Vero cells, without greatly affecting cell viability. We found that each of the agents decreased GFP fluorescence in the replicon cells, albeit to varying degrees. The agents other than rifapentine also showed a decrease in viral RNA levels in the replicon cells comparable to that seen for GFP fluorescence. These results indicate that persistent replication is susceptible to each of these five agents, although their mechanisms of action may differ. Taken together, these results provide evidence that translation/replication of the replicon in the replicon cells mimics that of the viral genome upon YFV 17D infection, indicating that the replicon cell lines can serve as a useful tool for high-throughput antiviral drug screening.

Nanoparticle- and Microparticle-Based Vaccines against Orbiviruses of Veterinary Importance

Bluetongue virus (BTV) and African horse sickness virus (AHSV) are widespread arboviruses that cause important economic losses in the livestock and equine industries, respectively. In addition to these, another arthropod-transmitted orbivirus known as epizootic hemorrhagic disease virus (EHDV) entails a major threat as there is a conducive landscape that nurtures its emergence in non-endemic countries. To date, only vaccinations with live attenuated or inactivated vaccines permit the control of these three viral diseases, although important drawbacks, e.g., low safety profile and effectiveness, and lack of DIVA (differentiation of infected from vaccinated animals) properties, constrain their usage as prophylactic measures. Moreover, a substantial number of serotypes of BTV, AHSV and EHDV have been described, with poor induction of cross-protective immune responses among serotypes. In the context of next-generation vaccine development, antigen delivery systems based on nano- or microparticles have gathered significant attention during the last few decades. A diversity of technologies, such as virus-like particles or self-assembled protein complexes, have been implemented for vaccine design against these viruses. In this work, we offer a comprehensive review of the nano- and microparticulated vaccine candidates against these three relevant orbiviruses. Additionally, we also review an innovative technology for antigen delivery based on the avian reovirus nonstructural protein muNS and we explore the prospective functionality of the nonstructural protein NS1 nanotubules as a BTV-based delivery platform.

Redirecting Imipramine against Bluetongue Virus Infection: Insights from a Genome-wide Haploid Screening Study

Bluetongue virus (BTV), an arbovirus of ruminants, is a causative agent of numerous epidemics around the world. Due to the emergence of novel reassortant BTV strains and new outbreaks, there is an unmet need for efficacious antivirals. In this study, we used an improved haploid screening platform to identify the relevant host factors for BTV infection. Our screening tool identified and validated the host factor Niemann–Pick C1 (NPC1), a lysosomal membrane protein that is involved in lysosomal cholesterol transport, as a critical factor in BTV infection. This finding prompted us to investigate the possibility of testing imipramine, an antidepressant drug known to inhibit NPC1 function by interfering with intracellular cholesterol trafficking. In this study, we evaluated the sensitivity of BTV to imipramine using in vitro assays. Our results demonstrate that imipramine pretreatment inhibited in vitro replication and progeny release of BTV-4, BTV-8, and BTV-16. Collectively, our findings highlight the importance of NPC1 for BTV infection and recommend the reprofiling of imipramine as a potential antiviral drug against BTV.

The Combined Expression of the Non-structural Protein NS1 and the N-Terminal Half of NS2 (NS21-180) by ChAdOx1 and MVA Confers Protection against Clinical Disease in Sheep upon Bluetongue Virus Challenge

Bluetongue, caused by bluetongue virus (BTV), is a widespread arthropod-borne disease of ruminants that entails a recurrent threat to the primary sector of developed and developing countries. In this work, we report modified vaccinia virus Ankara (MVA) and ChAdOx1-vectored vaccines designed to simultaneously express the immunogenic NS1 protein and/or NS2-Nt, the N-terminal half of protein NS2 (NS2_1-180). A single dose of MVA or ChAdOx1 expressing NS1-NS2-Nt improved the protection conferred by NS1 alone in IFNAR(-/-) mice. Moreover, mice immunized with ChAdOx1/MVA-NS1, ChAdOx1/MVA-NS2-Nt, or ChAdOx1/MVA-NS1-NS2-Nt developed strong cytotoxic CD8⁺ T-cell responses against NS1, NS2-Nt, or both proteins and were fully protected against a lethal infection with BTV serotypes 1, 4, and 8. Furthermore, although a single immunization with ChAdOx1-NS1-NS2-Nt partially protected sheep against BTV-4, the administration of a booster dose of MVA-NS1-NS2-Nt promoted a faster viral clearance, reduction of the period and level of viremia and also protected from the pathology produced by BTV infection.

IMPORTANCE Current BTV vaccines are effective but they do not allow to distinguish between vaccinated and infected animals (DIVA strategy) and are serotype specific. In this work we have develop a DIVA multiserotype vaccination strategy based on adenoviral (ChAdOx1) and MVA vaccine vectors, the most widely used in current phase I and II clinical trials, and the conserved nonstructural BTV proteins NS1 and NS2. This immunization strategy solves the major drawbacks of the current marketed vaccines.