Ribavirin efficiently suppresses porcine nidovirus replication

Antiviral activity of flavonol against porcine epidemic diarrhea virus

Porcine epidemic diarrhea virus (PEDV) remains one of the major causative microorganisms of viral diarrhea in piglets worldwide, with no approved drugs for treatment. We identified a natural molecule, flavonol, which is widely found in tea, vegetables and herbs. Subsequently, the antiviral activity of compound flavonol was evaluated in Vero cells and IPEC-J2 cells, and its anti-PEDV mechanism was analyzed by molecular docking and molecular dynamics. The results showed that flavonol could effectively inhibit viral progeny production, RNA synthesis and protein expression of PEDV strains in a dose-dependent manner. When flavonol was added simultaneously with viral infection in Vero cells, it demonstrated potent anti-PEDV activity by affecting the viral attachment and internalization phases. Similarly, in IPEC-J2 cells, flavonol effectively inhibited PEDV infection at different stages of infection, except for the release phase. Moreover, flavonol mainly interacts with PEDV Mpro through hydrogen bonds and hydrophobic forces, and the complex formed by it has high stability. Importantly, flavonol also showed broad-spectrum activity against other porcine enteric coronaviruses such as TGEV and PDCoV in vitro. These findings suggest that flavonol may exert antiviral effects by interacting with viral Mpro, thereby affecting viral replication. This means that flavonol is expected to become a potential drug to prevent or treat porcine enteric coronavirus.

The natural compound Sanggenon C inhibits PRRSV infection by regulating the TRAF2/NF-κB signalling pathway

Porcine reproductive and respiratory syndrome (PRRS) is a serious infectious disease and one of the major causes of death in the global pig industry. PRRS virus (PRRSV) strains have complex and diverse genetic characteristics and cross-protection between strains is low, which complicates vaccine selection; thus, the current vaccination strategy has been greatly compromised. Therefore, it is necessary to identify effective natural compounds for the clinical treatment of PRRS. A small molecule library composed of 720 natural compounds was screened in vitro, and we found that Sanggenon C (SC) was amongst the most effective natural compound inhibitors of PRRSV infection. Compared with ribavirin, SC more significantly inhibited PRRSV infection at both the gene and protein levels and reduced the viral titres and levels of protein expression and inflammatory cytokine secretion to more effectively protect cells from PRRSV infection and damage. Mechanistically, SC inhibits activation of the NF-κB signalling pathway by promoting TRAF2 expression, thereby reducing PRRSV replication. In conclusion, by screening natural compounds, we found that SC suppresses PRRSV infection by regulating the TRAF2/NF-κB signalling pathway. This study contributes to a deeper understanding of the therapeutic targets and pathogenesis of PRRSV infection. More importantly, our results demonstrate that SC has potential as a candidate for the treatment of PRRS.

Inhibiting mechanism of Alpiniae oxyphyllae fructus polysaccharide 3 against the replication of porcine epidemic diarrhea virus

Porcine epidemic diarrhea virus (PEDV) causes diarrhea, vomiting, and death in piglets. Our previous study has revealed the anti-PEDV activity of Alpiniae oxyphyllae fructus polysaccharide 3 (AOFP3). However, it is still unknown whether AOFP3 can inhibit the replication of PEDV. Therefore, the effect of AOFP3 on PEDV replication was investigated in the present study, along with analysis of viral RdRp activity and expression of hnRNP A1 by RNA polymerase activity assay in vitro, RIP assay, and Western blotting. The results showed that both the PEDV gene and protein levels in IPEC-J2 cells decreased with AOFP3 treatment. In addition, AOFP3 significantly reduced PEDV's replication by down-regulating the activity of PEDV RdRp and reducing the expression of hnRNP A1, whereas only the bind of RdRp to PEDV 3'UTR was inhibited in AOFP3 treated cells.

Toosendanin activates caspase-1 and induces maturation of IL-1β to inhibit type 2 porcine reproductive and respiratory syndrome virus replication via an IFI16-dependent pathway

Porcine reproductive and respiratory syndrome virus (PRRSV) is a prevalent and endemic swine pathogen which causes significant economic losses in the global swine industry. Multiple vaccines have been developed to prevent PRRSV infection. However, they provide limited protection. Moreover, no effective therapeutic drugs are yet available. Therefore, there is an urgent need to develop novel antiviral strategies to prevent PRRSV infection and transmission. Here we report that Toosendanin (TSN), a tetracyclic triterpene found in the bark or fruits of Melia toosendan Sieb. et Zucc., strongly suppressed type 2 PRRSV replication in vitro in Marc-145 cells and ex vivo in primary porcine alveolar macrophages (PAMs) at sub-micromolar concentrations. The results of transcriptomics revealed that TSN up-regulated the expression of IFI16 in Marc-145 cells. Furthermore, we found that IFI16 silencing enhanced the replication of PRRSV in Marc-145 cells and that the anti-PRRSV activity of TSN was dampened by IFI16 silencing, suggesting that the inhibition of TSN against PRRSV replication is IFI16-dependent. In addition, we showed that TSN activated caspase-1 and induced maturation of IL-1β in an IFI16-dependent pathway. To verify the role of IL-1β in PRRSV infection, we analyzed the effect of exogenous rmIL-1β on PRRSV replication, and the results showed that exogenous IL-1β significantly inhibited PRRSV replication in Marc-145 cells and PAMs in a dose-dependent manner. Altogether, our findings indicate that TSN significantly inhibits PRRSV replication at very low concentrations (EC₅₀: 0.16–0.20 μM) and may provide opportunities for developing novel anti-PRRSV agents.

Conserved coronavirus proteins as targets of broad-spectrum antivirals

Coronaviruses are a class of single-stranded, positive-sense RNA viruses that have caused three major outbreaks over the past two decades: Middle East respiratory syndrome–related coronavirus (MERS-CoV), severe acute respiratory syndrome coronavirus (SARS-CoV), and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). All outbreaks have been associated with significant morbidity and mortality. In this study, we have identified and explored conserved binding sites in the key coronavirus proteins for the development of broad-spectrum direct acting anti-coronaviral compounds and validated the significance of this conservation for drug discovery with existing experimental data. We have identified four coronaviral proteins with highly conserved binding site sequence and 3D structure similarity: PL^pro, M^pro, nsp10-nsp16 complex(methyltransferase), and nsp15 endoribonuclease. We have compiled all available experimental data for known antiviral medications inhibiting these targets and identified compounds active against multiple coronaviruses. The identified compounds representing potential broad-spectrum antivirals include: GC376, which is active against six viral M^pro (out of six tested, as described in research literature); mycophenolic acid, which is active against four viral PL^pro (out of four); and emetine, which is active against four viral RdRp (out of four). The approach described in this study for coronaviruses, which combines the assessment of sequence and structure conservation across a viral family with the analysis of accessible chemical structure – antiviral activity data, can be explored for the development of broad-spectrum drugs for multiple viral families.

Hypericin Inhibit Alpha-Coronavirus Replication by Targeting 3CL Protease

The porcine epidemic diarrhea virus (PEDV) is an Alphacoronavirus (α-CoV) that causes high mortality in infected piglets, resulting in serious economic losses in the farming industry. Hypericin is a dianthrone compound that has been shown as an antiviral activity on several viruses. Here, we first evaluated the antiviral effect of hypericin in PEDV and found the viral replication and egression were significantly reduced with hypericin post-treatment. As hypericin has been shown in SARS-CoV-2 that it is bound to viral 3CLpro, we thus established a molecular docking between hypericin and PEDV 3CLpro using different software and found hypericin bound to 3CLpro through two pockets. These binding pockets were further verified by another docking between hypericin and PEDV 3CLpro pocket mutants, and the fluorescence resonance energy transfer (FRET) assay confirmed that hypericin inhibits the PEDV 3CLpro activity. Moreover, the alignments of α-CoV 3CLpro sequences or crystal structure revealed that the pockets mediating hypericin and PEDV 3CLpro binding were highly conserved, especially in transmissible gastroenteritis virus (TGEV). We then validated the anti-TGEV effect of hypericin through viral replication and egression. Overall, our results push forward that hypericin was for the first time shown to have an inhibitory effect on PEDV and TGEV by targeting 3CLpro, and it deserves further attention as not only a pan-anti-α-CoV compound but potentially also as a compound of other coronaviral infections.

Drawing Comparisons between SARS-CoV-2 and the Animal Coronaviruses

The COVID-19 pandemic, caused by a novel zoonotic coronavirus (CoV), SARS-CoV-2, has infected 46,182 million people, resulting in 1,197,026 deaths (as of 1 November 2020), with devastating and far-reaching impacts on economies and societies worldwide. The complex origin, extended human-to-human transmission, pathogenesis, host immune responses, and various clinical presentations of SARS-CoV-2 have presented serious challenges in understanding and combating the pandemic situation. Human CoVs gained attention only after the SARS-CoV outbreak of 2002-2003. On the other hand, animal CoVs have been studied extensively for many decades, providing a plethora of important information on their genetic diversity, transmission, tissue tropism and pathology, host immunity, and therapeutic and prophylactic strategies, some of which have striking resemblance to those seen with SARS-CoV-2. Moreover, the evolution of human CoVs, including SARS-CoV-2, is intermingled with those of animal CoVs. In this comprehensive review, attempts have been made to compare the current knowledge on evolution, transmission, pathogenesis, immunopathology, therapeutics, and prophylaxis of SARS-CoV-2 with those of various animal CoVs. Information on animal CoVs might enhance our understanding of SARS-CoV-2, and accordingly, benefit the development of effective control and prevention strategies against COVID-19.

Matrine exhibits antiviral activity in a PRRSV/PCV2 co-infected mouse model

BACKGROUND

PRRSV and PCV2 co-infection is very common in swine industry which results in huge economic losses worldwide. Although vaccination is used to prevent viral diseases, immunosuppression induced by PRRSV and PCV2 leads to vaccine failure.

PURPOSE

Our previous results have demonstrated that Matrine possess antiviral activities against PRRSV/PCV2 co-infection in vitro. This study aims to establish a PRRSV/PCV2 co-infected KM mouse model and evaluate the antiviral activities of Matrine against PRRSV/PCV2 co-infection.

STUDY DESIGN

A total of 144 KM mice were randomly divided into six groups with 24 mice in each group, named as: normal control, PRRSV/PCV2 co-infected group (PRRSV/PCV2 group), Ribavirin treatment positive control (Ribavirin control) and Matrine treatment groups (Matrine 40 mg/kg, Matrine 20 mg/kg and Matrine 10 mg/kg).

METHODS

Except normal control group, all mice in other five groups were inoculated with PRRSV, followed by PCV2 at 2 h later. At 7 days post-infection (dpi), mice in the treatment groups were intraperitoneally administered with various doses of Matrine and Ribavirin, twice a day for 5 consecutive days.

RESULTS

PRRSV N and PCV2 CAP genes were detected by PCR in multiple tissues including heart, liver, spleen, lungs, kidneys, thymus and inguinal lymph nodes. The viral load of PCV2 was the highest in liver followed by thymus and spleen. Although PRRSV were detected in most of tissues, but the replication of PRRSV was not significantly increased, as shown by qPCR analysis. Comparing with PCV2 infection alone, PRRSV infection significantly elevated PCV2 replication and exacerbated PCV2 induced interstitial pneumonia. qPCR analysis demonstrated 40 mg/kg Matrine significantly attenuated PCV2 replication in liver and alleviated virus induced interstitial pneumonia, suggesting Matrine could directly inhibit virus replication. In addition, Matrine treatment enhanced peritoneal macrophages phagocytosis at 13 and 16 dpi, and 40 mg/kg of Matrine increased the proliferation activity of lymphocytes. Body weight gain was continuously promoted by administrating Matrine at 10 mg/kg.

CONCLUSION

Matrine possessed antiviral activities via inhibiting virus replication and regulating immune functions in mice co-infected by PRRSV/PCV2. These data provide new insight into controlling PRRSV and PCV2 infection and support further research for developing Matrine as a new possible veterinary medicine.

Replication of Equine arteritis virus is efficiently suppressed by purine and pyrimidine biosynthesis inhibitors

RNA viruses are responsible for a large variety of animal infections. Equine Arteritis Virus (EAV) is a positive single-stranded RNA virus member of the family Arteriviridae from the order Nidovirales like the Coronaviridae. EAV causes respiratory and reproductive diseases in equids. Although two vaccines are available, the vaccination coverage of the equine population is largely insufficient to prevent new EAV outbreaks around the world. In this study, we present a high-throughput in vitro assay suitable for testing candidate antiviral molecules on equine dermal cells infected by EAV. Using this assay, we identified three molecules that impair EAV infection in equine cells: the broad-spectrum antiviral and nucleoside analog ribavirin, and two compounds previously described as inhibitors of dihydroorotate dehydrogenase (DHODH), the fourth enzyme of the pyrimidine biosynthesis pathway. These molecules effectively suppressed cytopathic effects associated to EAV infection, and strongly inhibited viral replication and production of infectious particles. Since ribavirin is already approved in human and small animal, and that several DHODH inhibitors are in advanced clinical trials, our results open new perspectives for the management of EAV outbreaks.

Porcine deltacoronavirus activates the Raf/MEK/ERK pathway to promote its replication

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PDCoV activated the ERK signaling pathway irrespective of viral replication.

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Chemical inhibition and ERK1/2 knockdown markedly impaired PDCoV biosynthesis.

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Cellular and viral cholesterols were involved to PDCoV-induced ERK activation.

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There was no crosstalk between ERK and apoptotic pathways during PDCoV infection.

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PDCoV exploits the ERK cascade to complete successful viral infection.

Porcine deltacoronavirus (PDCoV) is a newly emerged swine coronavirus that causes acute enteritis in neonatal piglets. To date, little is known about the host factors or cellular signaling mechanisms associated with PDCoV replication. Since the Raf/MEK/ERK pathway is involved in modulation of various important cellular functions, numerous DNA and RNA viruses coopt this pathway for efficient propagation. In the present study, we found that PDCoV induces the activation of ERK1/2 and its downstream substrate Elk-1 early in infection irrespective of viral biosynthesis. Chemical inhibition or knockdown of ERK1/2 significantly suppressed viral replication, whereas treatment with an ERK activator increased viral yields. Direct pharmacological inhibition of ERK activation had no effect on the viral entry process but sequentially affected the post-entry steps of the virus life cycle. In addition, pharmacological sequestration of cellular or viral cholesterol downregulated PDCoV-induced ERK signaling, highlighting the significance of the cholesterol contents in ERK activation. However, ERK inhibition had no effect on PDCoV-triggered apoptosis through activation of the cytochrome c-mediated intrinsic mitochondrial pathway, suggesting the irrelevance of ERK activation to the apoptosis pathway during PDCoV infection. Altogether, our findings indicate that the ERK signaling pathway plays a pivotal role in viral biosynthesis to facilitate the optimal replication of PDCoV.

Hepatitis E virus (HEV)-The Future

Hepatitis (HEV) is widely distributed in pigs and is transmitted with increasing numbers to humans by contact with pigs, contaminated food and blood transfusion. The virus is mostly apathogenic in pigs but may enhance the pathogenicity of other pig viruses. In humans, infection can lead to acute and chronic hepatitis and extrahepatic manifestations. In order to stop the emerging infection, effective counter-measures are required. First of all, transmission by blood products can be prevented by screening all blood donations. Meat and sausages should be appropriately cooked. Elimination of the virus from the entire pork production can be achieved by sensitive testing and elimination programs including early weaning, colostrum deprivation, Caesarean delivery, embryo transfer, treatment with antivirals, protection from de novo infection, and possibly vaccination. In addition, contaminated water, shellfish, vegetables, and fruits by HEV-contaminated manure should be avoided. A special situation is given in xenotransplantation using pig cells, tissues or organs in order to alleviate the lack of human transplants. The elimination of HEV from pigs, other animals and humans is consistent with the One Health concept, preventing subclinical infections in the animals as well as preventing transmission to humans and disease.

Growth enhancement of porcine epidemic diarrhea virus (PEDV) in Vero E6 cells expressing PEDV nucleocapsid protein

More recently emerging strains of porcine epidemic diarrhea virus (PEDV) cause severe diarrhea and especially high mortality rates in infected piglets, leading to substantial economic loss to worldwide swine industry. These outbreaks urgently call for updated and effective PEDV vaccines. Better understanding in PEDV biology and improvement in technological platforms for virus production can immensely assist and accelerate PEDV vaccine development. In this study, we explored the ability of PEDV nucleocapsid (N) protein in improving viral yields in cell culture systems. We demonstrated that PEDV N expression positively affected both recovery of PEDV from infectious clones and PEDV propagation in cell culture. Compared to Vero E6 cells, Vero E6 cells expressing PEDV N could accelerate growth of a slow-growing PEDV strain to higher peak titers by 12 hours or enhance the yield of a vaccine candidate strain by two orders of magnitude. Interestingly, PEDV N also slightly enhances replication of porcine reproductive and respiratory virus, a PEDV relative in the Nidovirales order. These results solidify the importance of N in PEDV recovery and propagation and suggest a potentially useful consideration in designing vaccine production platforms for PEDV or closely related pathogens.

Ribavirin-induced mutagenesis across the complete open reading frame of hepatitis C virus genotypes 1a and 3a

Ribavirin (RBV) has been used for the last 20 years to treat patients with chronic hepatitis C virus (HCV) infection. This pluripotent drug is believed to induce mutagenesis in HCV RNA. However, for cell-cultured HCV (HCVcc) this phenomenon has only been investigated in genotype 2a recombinants. Here we studied the mutations that developed in HCVcc of genotypes 1a and 3a treated with RBV or ribavirin triphosphate (RBV-TP) compared to non-treated controls. Analysis was performed on the amplified full-length open reading frame (ORF) of recovered viruses following next-generation sequencing and clonal analyses. Compared to non-treated controls, the spread of TNcc(1a) and DBN3acc(3a) HCVcc was delayed by RBV and RBV-TP at concentrations of 40 µM or higher. The delay in HCVcc spread was associated with increased new single-nucleotide polymorphisms (SNP). Significantly higher numbers of new SNP were observed in TNcc(1a) viruses treated with RBV or RBV-TP compared to matched non-treated controls. RBV or RBV-TP treatment led to significantly increased proportions of new G-to-A and C-to-U SNP compared to non-treated TNcc(1a). Clonal analyses confirmed a significantly increased mutation rate in RBV-treated TNcc(1a). Synonymous pairwise distances increased in both viruses across the complete ORF under RBV and RBV-TP treatment compared to controls. Consensus-shifts in single samples of RBV- or RBV-TP-treated TNcc(1a) viruses occurred in proteins E1, p7, NS3 and NS4B. No non-synonymous consensus changes were observed in DBN3acc(3a). This study supports a biased G-to-A and C-to-U mutagenic effect of RBV and RBV-TP throughout the entire ORF of HCV genotypes 1a and 3a.

Identification of Inhibitory Compounds Against Singapore Grouper Iridovirus Infection by Cell Viability-Based Screening Assay and Droplet Digital PCR

Singapore grouper iridovirus (SGIV) is one of the major causative agents of fish diseases and has caused significant economic losses in the aquaculture industry. There is currently no commercial vaccine or effective antiviral treatment against SGIV infection. Annually, an increasing number of small molecule compounds from various sources have been produced, and many are proved to be potential inhibitors against viruses. Here, a high-throughput in vitro cell viability-based screening assay was developed to identify antiviral compounds against SGIV using the luminescent-based CellTiter-Glo reagent in cultured grouper spleen cells by quantificational measurement of the cytopathic effects induced by SGIV infection. This assay was utilized to screen for potential SGIV inhibitors from five customized compounds which had been reported to be capable of inhibiting other viruses and 30 compounds isolated from various marine organisms, and three of them [ribavirin, harringtonine, and 2-hydroxytetradecanoic acid (2-HOM)] were identified to be effective on inhibiting SGIV infection, which was further confirmed with droplet digital PCR (ddPCR). In addition, the ddPCR results revealed that ribavirin and 2-HOM inhibited SGIV replication and entry in a dose-dependent manner, and harringtonine could reduce SGIV replication rather than entry at the working concentration without significant toxicity. These findings provided an easy and reliable cell viability-based screening assay to identify compounds with anti-SGIV effect and a way of studying the anti-SGIV mechanism of compounds.

Cellular cholesterol is required for porcine nidovirus infection

Porcine reproductive and respiratory syndrome virus (PRRSV) and porcine epidemic diarrhea virus (PEDV) are porcine nidoviruses that are considered emerging and re-emerging viral pathogens of pigs that pose a significant economic threat to the global pork industry. Although cholesterol is known to affect the replication of a broad range of viruses in vitro, its significance and role in porcine nidovirus infection remains to be elucidated. Therefore, the present study was conducted to determine whether cellular or/and viral cholesterol levels play a role in porcine nidovirus infection. Our results showed that depletion of cellular cholesterol by treating cells with methyl-β-cyclodextrin (MβCD) dose-dependently suppressed the replication of both nidoviruses. Conversely, cholesterol depletion from the viral envelope had no inhibitory effect on porcine nidovirus production. The addition of exogenous cholesterol to MβCD-treated cells moderately restored the infectivity of porcine nidoviruses, indicating that the presence of cholesterol in the target cell membrane is critical for viral replication. The antiviral activity of MβCD on porcine nidovirus infection was found to be predominantly exerted when used as a treatment pre-infection or prior to the viral entry process. Furthermore, pharmacological sequestration of cellular cholesterol efficiently blocked both virus attachment and internalization and, accordingly, markedly affected subsequent post-entry steps of the replication cycle, including viral RNA and protein biosynthesis and progeny virus production. Taken together, our data indicate that cell membrane cholesterol is required for porcine nidovirus entry into cells, and pharmacological drugs that hamper cholesterol-dependent virus entry may have antiviral potential against porcine nidoviruses.

Identification of two mutation sites in spike and envelope proteins mediating optimal cellular infection of porcine epidemic diarrhea virus from different pathways

Entry of the α-coronavirus porcine epidemic diarrhea virus (PEDV) requires specific proteases to activate spike (S) protein for the membrane fusion of the virion to the host cell following receptor binding. Herein, PEDV isolate 85-7 could proliferate and induce cell-cell fusion in a trypsin independent manner on Vero cells, and eight homologous mutation strains were screened by continuous proliferation in the absence of trypsin on Vero cells. According to the whole genome sequence comparative analysis, we identified four major variations located in nonstructural protein 2, S, open reading frame 3, and envelope (E) genes, respectively. Comparative analyses of their genomic variations and proliferation characteristics identified a single mutation within the S2' cleavage site between C30 and C40 mutants: the substitution of conserved arginine (R) by a glycine (G) (R895G). This change resulted in weaker cell-cell fusion, smaller plaque morphology, higher virus titer and serious microfilament condensation. Further analysis confirmed that this mutation was responsible for optimal cell-adaptation, but not the determinant for trypsin-dependent entry of PEDV. Otherwise, a novel variation (16-20 aa deletion and an L25P mutation) in the transmembrane domain of the E protein affected multiple infection processes, including up-regulation of the production of the ER stress indicator GRP78, improving the expression of pro-inflammatory cytokines IL-6 and IL-8, and promoting apoptosis. The results of this study provide a better understanding of the potential mechanisms of viral functional proteins in PEDV replication, infection, and fitness.

Rapamycin-induced autophagy restricts porcine epidemic diarrhea virus infectivity in porcine intestinal epithelial cells

Porcine epidemic diarrhea virus (PEDV) invades porcine intestinal epithelial cells (IECs) and causes diarrhea and dehydration in pigs. In the present study, we showed a suppression of PEDV infection in porcine jejunum intestinal epithelial cells (IPEC-J2) by an increase in autophagy. Autophagy was activated by rapamycin at a dose that does not affect cell viability and tight junction permeability. The induction of autophagy was examined by LC3I/LC3II conversion. To confirm the autophagic-flux (entire autophagy pathway), autophagolysosomes were examined by an immunofluorescence assay. Pre-treatment with rapamycin significantly restricted not only a 1 h infection but also a longer infection (24 h) with PEDV, while this effect disappeared when autophagy was blocked. Co-localization of PEDV and autophagosomes suggests that PEDV could be a target of autophagy. Moreover, alleviation of PEDV-induced cell death in IPEC-J2 cells pretreated with rapamycin demonstrates a protective effect of rapamycin against PEDV-induced epithelial cell death. Collectively, the present study suggests an early prevention against PEDV infection in IPEC-J2 cells via autophagy that might be an effective strategy for the restriction of PEDV, and opens up the possibility of the use of rapamycin in vivo as an effective prophylactic and prevention treatment.

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Rapamycin has an antiviral effect against PEDV infection.

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Rapamycin prevents PEDV-induced cell death.

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Rapamycin-induced autophagy restricted PEDV infection in porcine intestinal epithelial cells.

Hematological adverse effects and pharmacokinetics of ribavirin in pigs following intramuscular administration

Ribavirin (RBV) is a synthetic guanosine analog that is used as a drug against various viral diseases in humans. The in vitro antiviral effects of ribavirin against porcine viruses were demonstrated in several studies. The purposes of this study were to evaluate the adverse effects and pharmacokinetics of ribavirin following its intramuscular (IM) injection in pigs. Ribavirin was formulated as a double-oil emulsion (RBV-DOE) and gel (RBV-Gel), which were injected into the pigs as single-dose IM injections. After injection of RBV, all of the pigs were monitored. The collected serum and whole blood samples were analyzed by liquid chromatography-tandem mass spectrometry and complete blood count analysis, respectively. All of the ribavirin-treated pigs showed significant decreases in body weight compared to the control groups. Severe clinical signs including dyspnea, anorexia, weakness, and depression were present in ribavirin-treated pigs until 5 days postinjection (dpi). The ribavirin-treated groups showed significant decrease in the number of red blood cells and hemoglobin concentration until 8 dpi. The mean half-life of the RBV-DOE and RBV-Gel was 27.949 ± 2.783 h and 37.374 ± 3.502 h, respectively. The mean peak serum concentration (C_max ) and area under the serum concentration-time curve from time zero to infinity (AUC_inf ) of RBV-DOE were 8340.000 ± 2562.577 ng/mL and 16 0095.430 ± 61 253.400 h·ng/mL, respectively. The C_max and AUC_inf of RBV-Gel were 15 300.000 ± 3764.306 ng/mL and 207526.260 ± 63656.390 h·ng/mL, respectively. The results of this study provided the index of side effect and pharmacokinetics of ribavirin in pigs, which should be considered before clinical application.

Nidovirus RNA polymerases: Complex enzymes handling exceptional RNA genomes

Coronaviruses and arteriviruses are distantly related human and animal pathogens that belong to the order Nidovirales. Nidoviruses are characterized by their polycistronic plus-stranded RNA genome, the production of subgenomic mRNAs and the conservation of a specific array of replicase domains, including key RNA-synthesizing enzymes. Coronaviruses (26-34 kilobases) have the largest known RNA genomes and their replication presumably requires a processive RNA-dependent RNA polymerase (RdRp) and enzymatic functions that suppress the consequences of the typically high error rate of viral RdRps. The arteriviruses have significantly smaller genomes and form an intriguing package with the coronaviruses to analyse viral RdRp evolution and function. The RdRp domain of nidoviruses resides in a cleavage product of the replicase polyprotein named non-structural protein (nsp) 12 in coronaviruses and nsp9 in arteriviruses. In all nidoviruses, the C-terminal RdRp domain is linked to a conserved N-terminal domain, which has been coined NiRAN (nidovirus RdRp-associated nucleotidyl transferase). Although no structural information is available, the functional characterization of the nidovirus RdRp and the larger enzyme complex of which it is part, has progressed significantly over the past decade. In coronaviruses several smaller, non-enzymatic nsps were characterized that direct RdRp function, while a 3'-to-5' exoribonuclease activity in nsp14 was implicated in fidelity. In arteriviruses, the nsp1 subunit was found to maintain the balance between genome replication and subgenomic mRNA production. Understanding RdRp behaviour and interactions during RNA synthesis and subsequent processing will be key to rationalising the evolutionary success of nidoviruses and the development of antiviral strategies.

JNK and p38 mitogen-activated protein kinase pathways contribute to porcine epidemic diarrhea virus infection

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PEDV infection activated p38 MAPK and JNK1/2 in vitro.

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UV-inactivated virus failed to induce p38 MAPK and JNK1/2 activation.

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Pharmacological inhibition of p38 MAPK or JNK activation impaired PEDV replication.

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SAPK cascades do not affect the apoptosis pathway during PEDV infection.

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PEDV exploits the p38 MAPK and JNK signaling pathways for optimal replication.

The mitogen-activated protein kinase (MAPK) pathways, which are central building blocks in the intracellular signaling network, are often manipulated by viruses of diverse families to favor their replication. Among the MAPK family, the extracellular signal-regulated kinase (ERK) pathway is known to be modulated during the infection with porcine epidemic diarrhea virus (PEDV); however, involvement of stress-activated protein kinases (SAPKs) comprising p38 MAPK and c-Jun NH₂-terminal kinase (JNK) remains to be determined. Therefore, in the present study, we investigated whether activation of p38 MAPK and JNK cascades is required for PEDV replication. Our results showed that PEDV activates p38 MAPK and JNK1/2 up to 24 h post-infection, whereas, thereafter their phosphorylation levels recede to baseline levels or even fall below them. Notably, UV-irradiated inactivated PEDV, which can enter cells but cannot replicate inside them, failed to induce phosphorylation of p38 MAPK and JNK1/2 suggesting that viral biosynthesis is essential for activation of these kinases. Treatment of cells with selective p38 or JNK inhibitors markedly impaired PEDV replication in a dose-dependent manner and these antiviral effects were found to be maximal during the early times of the infection. Furthermore, direct pharmacological inhibition of p38 MAPK or JNK1/2 activation resulted in a significant reduction of viral RNA synthesis, viral protein expression, and progeny release. However, independent treatments with either SAPK inhibitor did not inhibit PEDV-induced apoptotic cell death mediated by activation of mitochondrial apoptosis-inducing factor (AIF) suggesting that SAPKs are irrelevant to the apoptosis pathway during PEDV infection. In summary, our data demonstrated critical roles of the p38 and JNK1/2 signaling pathways in facilitating successful viral infection during the post-entry steps of the PEDV life cycle.

Matrine displayed antiviral activity in porcine alveolar macrophages co-infected by porcine reproductive and respiratory syndrome virus and porcine circovirus type 2

The co-infection of porcine reproductive respiratory syndrome virus (PRRSV) and porcine circovirus type 2 (PCV2) is quite common in clinical settings and no effective treatment to the co-infection is available. In this study, we established the porcine alveolar macrophages (PAM) cells model co-infected with PRRSV/PCV2 with modification in vitro, and investigated the antiviral activity of Matrine on this cell model and further evaluated the effect of Matrine on virus-induced TLR3,4/NF-κB/TNF-α pathway. The results demonstrated PAM cells inoculated with PRRSV followed by PCV2 2 h later enhanced PRRSV and PCV2 replications. Matrine treatment suppressed both PRRSV and PCV2 infection at 12 h post infection. Furthermore, PRRSV/PCV2 co- infection induced IκBα degradation and phosphorylation as well as the translocation of NF-κB from the cytoplasm to the nucleus indicating that PRRSV/PCV2 co-infection induced NF-κB activation. Matrine treatment significantly down-regulated the expression of TLR3, TLR4 and TNF-α although it, to some extent, suppressed p-IκBα expression, suggesting that TLR3,4/NF-κB/TNF-α pathway play an important role of Matrine in combating PRRSV/PCV2 co-infection. It is concluded that Matrine possesses activity against PRRSV/PCV2 co-infection in vitro and suppression of the TLR3,4/NF-κB/TNF-α pathway as an important underlying molecular mechanism. These findings warrant Matrine to be further explored for its antiviral activity in clinical settings.

Pharmacokinetics, efficacy prediction indexes, and residue depletion of ribavirin in Atlantic salmon's (Salmo salar) muscle after oral administration in feed

Ribavirin is an antiviral used in human medicine, but it has not been authorized for use in veterinary medicine although it is effective against infectious salmon anemia (ISA) virus, between others. In this study, we present a pharmacokinetic profile of ribavirin in Atlantic salmon (Salmo salar), efficacy prediction indexes, and the measure of its withdrawal time. To determine the pharmacokinetic profile, fishes were orally administered with a single ribavirin dose of 1.6 mg/kg bw, and then, plasma concentrations were measured at different times. From the time-vs.-concentration curve, Cmax = 413.57 ng/mL, Tmax  = 6.96 h, AUC = 21394.01 μg·h/mL, t1/2  = 81.61 h, and K10  = 0.0421/h were obtained. Ribavirin reached adequate concentrations during the pharmacokinetic study, with prediction indexes of Cmax /IC50  = 20.7, AUC/IC50  = 1069.7, and T>IC50  = 71 h, where IC is the inhibitory concentration 50%. For ribavirin depletion study, fishes were orally administered with a dairy dose of 1.6 mg/kg bw during 10 days. Concentrations were measured on edible tissue on different days post-treatment. A linear regression of the time vs. concentration was conducted, obtaining a withdrawal time of 1966 °C days. Results obtained reveal that the dose of 1.6 mg/kg bw orally administered is effective for ISA virus, originating a reasonable withdrawal period within the productive schedules of Atlantic salmon.

Trends in Antiviral Strategies

Viral populations are true moving targets regarding the genomic sequences to be targeted in antiviral designs. Experts from different fields have expressed the need of new paradigms for antiviral interventions and viral disease control. This chapter reviews several strategies that aim at counteracting the adaptive capacity of viral quasispecies. The proposed designs are based on combinations of different antiviral drugs and immune modulators, or in the administration of virus-specific mutagenic agents, in an approach termed lethal mutagenesis of viruses. It consists of decreasing viral fitness by an excess of mutations that render viral proteins sub-optimal or non-functional. Viral extinction by lethal mutagenesis involves several sequential, overlapping steps that recapitulate the major concepts of intra-population interactions and genetic information stability discussed in preceding chapters. Despite the magnitude of the challenge, the chapter closes with some optimistic prospects for an effective control of viruses displaying error-prone replication, based on the combined targeting of replication fidelity and the induction of the innate immune response.

Porcine epidemic diarrhea virus: An emerging and re-emerging epizootic swine virus

The enteric disease of swine recognized in the early 1970s in Europe was initially described as “epidemic viral diarrhea” and is now termed “porcine epidemic diarrhea (PED)”. The coronavirus referred to as PED virus (PEDV) was determined to be the etiologic agent of this disease in the late 1970s. Since then the disease has been reported in Europe and Asia, but the most severe outbreaks have occurred predominantly in Asian swine-producing countries. Most recently, PED first emerged in early 2013 in the United States that caused high morbidity and mortality associated with PED, remarkably affecting US pig production, and spread further to Canada and Mexico. Soon thereafter, large-scale PED epidemics recurred through the pork industry in South Korea, Japan, and Taiwan. These recent outbreaks and global re-emergence of PED require urgent attention and deeper understanding of PEDV biology and pathogenic mechanisms. This paper highlights the current knowledge of molecular epidemiology, diagnosis, and pathogenesis of PEDV, as well as prevention and control measures against PEDV infection. More information about the virus and the disease is still necessary for the development of effective vaccines and control strategies. It is hoped that this review will stimulate further basic and applied studies and encourage collaboration among producers, researchers, and swine veterinarians to provide answers that improve our understanding of PEDV and PED in an effort to eliminate this economically significant viral disease, which emerged or re-emerged worldwide.

Anti-PRRSV effect and mechanism of tetrahydroaltersolanol C in vitro

Porcine reproductive and respiratory syndrome virus (PRRSV) is an important arterivirus that causes substantial economic losses to the swine industry. Current control strategies against PRRSV are still inadequate and there is an urgent need for new antiviral therapies. Tetrahydroaltersolanol C (TD-C) is a new anthraquinone derivative isolated from the marine-derived fungi. In the present study, we first demonstrated its anti-PRRSV activity in vitro through assessing the inhibition of TD-C on cytopathic effect, viral ORF7 gene and N protein expressions, progeny virions production by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, relative-quantitative RT-PCR, Western blotting, and indirect immunofluorescence assay. Our experimental results showed that TD-C could significantly inhibit PRRSV replication in a dose-dependent manner. The 50% effective concentration, 50% cytotoxic concentration and the selectivity index were 12.11, 395.31 μM, and 32.64, respectively. Furthermore, the possible anti-PRRSV mechanism was explored by virucidal assay, virus adsorption inhibition assay, and the time-of-addition assay. The results showed that TD-C might inhibit the internalization and replication of PRRSV, but did not directly inactivate the virus or block its adsorption to cell surface. In conclusion, our findings indicated that TD-C possessed a significant anti-PRRSV activity, and provided a strong basis for further exploration of this compound as an antiviral agent against PRRSV.

Amino acid residues Ala283 and His421 in the RNA-dependent RNA polymerase of porcine reproductive and respiratory syndrome virus play important roles in viral ribavirin sensitivity and quasispecies diversity

The quasispecies diversity of RNA viruses is mainly determined by the fidelity of RNA-dependent RNA polymerase (RdRp) during viral RNA replication. Certain amino acid residues play an important role in determining the fidelity, and such residues can be substituted with other amino acids to produce virus strains with higher fidelity. In this study, two amino acid substitutions (A283T and H421Y) in the RdRp of porcine reproductive and respiratory syndrome virus (PRRSV) were identified under the selection of ribavirin. Preliminary data showed that two substitutions were involved in conferring PRRSV with the properties of increased ribavirin resistance and restricted quasispecies diversity. The results indicated that these two amino acid residues (Ala283 and His421) play a crucial role in PRRSV replication by affecting the fidelity of its RdRp. The results have important implications for understanding the molecular mechanism of PRRSV evolution and pathogenicity, and developing a safer modified live-attenuated vaccine (MLV) against PRRSV.

Preventing transfer of infectious agents

Xenotransplantation using pig cells, tissues and organs may be associated with the transfer of porcine infectious agents, which may infect the human recipient and in the worst case induce a disease (zoonosis). To prevent this, a broad screening program of the donor animals for putative zoonotic microorganisms, including bacteria, viruses, fungi and others, using sensitive and specific detection methods has to be performed. As long as it is still unknown, which microorganism represents a real risk for the recipient, experience from allotransplantation should be brought in. Due to the fact that pigs can be screened long before the date of transplantation, xenotransplantation will become eventually safer compared with allotransplantation. Screening and selection of animals free of potential zoonotic microorganisms, Caesarean section, vaccination and/or treatment with chemotherapeutics are the strategies of choice to obtain donor animals not transmitting microorganisms. In the case of porcine endogenous retroviruses (PERVs) which are integrated in the genome of all pigs and which cannot be eliminated this way, selection of animals with low virus expression and generation of genetically modified pigs suppressing PERV expressions may be performed.

Extracellular signal-regulated kinase (ERK) activation is required for porcine epidemic diarrhea virus replication

Porcine epidemic diarrhea virus (PEDV) is a highly enteropathogenic coronavirus of swine that causes acute enteritis with high mortality in nursery piglets. To date, the cellular factors involved in PEDV replication have not been well defined. The extracellular signal-regulated kinase (ERK) that serves as a critical component of cellular signal transduction pathways to modulate a variety of cellular functions has been shown to regulate several viral infections. In the present study, we found that PEDV activates ERK1/2 early in infection independently of viral replication. The PEDV-induced ERK1/2 activation resulted in the phosphorylation of its downstream substrate Elk-1 in infected cells. Treatment with ERK inhibitors or ERK1/2 knockdown significantly suppressed viral progeny production. Inhibition of ERK activation also diminished viral protein expression and genomic and subgenomic RNA transcription. These findings indicate that the ERK signaling pathway plays an important role in the PEDV life cycle and beneficially contributes to viral infection.

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PEDV infection activates the ERK signaling pathway in vitro.

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PEDV phosphorylates the ERK downstream substrate Elk-1.

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Chemical inhibition and ERK1/2 knockdown impairs the replication of PEDV.

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ERK activation is not associated with PEDV-induced apoptotic cell death.

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The ERK signaling pathway plays a central role in PEDV replication.

Functional characterization and proteomic analysis of the nucleocapsid protein of porcine deltacoronavirus

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The PDCoV N protein exists as non-covalently linked oligomers.

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PDCoV N is predominantly distributed in the nucleolus.

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N overexpression had no effect on cell growth.

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PDCoV N significantly altered two cellular chaperone proteins, GRP78 and HSC70.

Porcine deltacoronavirus (PDCoV) is a newly discovered enterotropic swine coronavirus that causes enteritis and diarrhea in piglets. Like other coronaviruses, PDCoV commonly contains 4 major structural proteins: spike (S), envelope (E), membrane (M), and nucleocapsid (N) proteins. Among these, the N protein is known to be the most abundant and multifunctional viral component. Therefore, as the first step toward understanding the biology of PDCoV, the present study investigated functional characteristics and expression dynamics of host proteins in a stable porcine cell line constitutively expressing the PDCoV N protein. Similar to N proteins of other coronaviruses, the PDCoV N protein was found to interact with itself to form non-covalently linked oligomers and was mainly localized to the nucleolus. We then assessed alterations in production levels of proteins in the N-expressing PK (PK-PDCoV-N) cells at different time points by means of proteomic analysis. According to the results of high-resolution two-dimensional gel electrophoresis, a total of 43 protein spots were initially found to be differentially expressed in PK-PDCoV-N cells in comparison with control PK cells. Of these spots, 10 protein spots showed a statistically significant alteration, including 8 up-regulated and 2 down-regulated protein spots and were picked for subsequent protein identification by peptide mass fingerprinting following matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The affected cellular proteins that we identified in this study were classified into the functional groups involved in various cellular processes such as cell division, metabolism, the stress response, protein biosynthesis and transport, cytoskeleton networks and cell communication. Notably, two members of the heat shock protein 70 family were found to be up-regulated in PK-PDCoV-N cells. These proteomic data will provide insights into the specific cellular response to the N protein during PDCoV infection.

Analysis of protein expression changes of the Vero E6 cells infected with classic PEDV strain CV777 by using quantitative proteomic technique

Recent outbreaks of porcine epidemic diarrhea virus (PEDV) have caused widespread concern. The identification of proteins associated with PEDV infection might provide insight into PEDV pathogenesis and facilitate the development of novel antiviral strategies. We analyzed the differential protein profile of PEDV-infected Vero E6 cells using mass spectrometry and an isobaric tag for relative and absolute quantification. A total of 126 proteins were identified that were differentially expressed between the PEDV-infected and mock-infected groups (P<0.05, quantitative ratio ≥1.2), among which the expression of 58 proteins was up-regulated and that of 68 proteins was down-regulated in the PEDV-infected Vero E6 cells, involving in integrin β2/β3, cystatin-C. The Gene Ontology analysis indicated that the molecular function of the differentially expressed proteins (DEPs) was primarily related to binding and catalytic activity, and that the biological functions in which the DEPs are involved included metabolism, organismal systems, cellular processes, genetic information processing, environmental information processing, and diseases. Among the disease-related functions, certain anti-viral pathways and proteins, such as the RIG-I-like receptor, Rap1, autophagy, mitogen-activated protein kinase, PI3K-Akt and Jak-STAT signaling pathways, and integrin β2/β3 and cystatin-C proteins, represented potential factors in PEDV infection. Our findings provide valuable insight into PEDV-Vero E6 cell interactions.

Xenotransplantation and Hepatitis E virus

Xenotransplantation using pig cells, tissues and organs may be associated with the transmission of porcine microorganisms to the human recipient. Some of these microorganisms may induce a zoonosis, that is an infectious disease induced by microorganisms transmitted from another species. With exception of the porcine endogenous retroviruses (PERVs), which are integrated in the genome of all pigs, the transmission of all other microorganisms can be prevented by specified or designated pathogen-free (spf or dpf, respectively) production of the animals. However, it is becoming clear in the last years that the hepatitis E virus (HEV) is one of the viruses which are difficult to eliminate. It is important to note that there are differences between HEV of genotypes (gt) 1 and gt2 on one hand and HEV of gt3 and gt4 on the other. HEV gt1 and gt2 are human viruses, and they induce hepatitis and in the worst case fatal infections in pregnant women. In contrast, HEV gt3 and gt4 are viruses of pigs, and they may infect humans, induce commonly only mild diseases, if any, and are harmless for pregnant women. The goal of this review was to evaluate the risk posed by HEV gt3 and gt4 for xenotransplantation and to indicate ways of their elimination from pigs in order to prevent transmission to the human recipient.

Effects of ribavirin on the replication and genetic stability of porcine reproductive and respiratory syndrome virus

Background

Although modified live virus (MLV) vaccines are commonly used for porcine reproductive and respiratory syndrome virus (PRRSV) control, there have been safety concerns due to the quick reversion of MLV to virulence during replication in pigs. Previous studies have demonstrated that mutant viruses emerged from lethal mutagenesis driven by antiviral mutagens and that those viruses had higher genetic stability compared to their parental strains because they acquired resistance to random mutation. Thus, this strategy was explored to stabilize the PRRSV genome in the current study.

Results

Four antiviral mutagens (ribavirin, 5-fluorouracil, 5-azacytidine, and amiloride) were evaluated for their antiviral effects against VR2332, a prototype of type 2 PRRSV. Among the mutagens, ribavirin and 5-fluorouracil had significant antiviral effects against VR2332. Consequently, VR2332 was serially passaged in MARC-145 cells in the presence of ribavirin at several concentrations to facilitate the emergence of ribavirin-resistant mutants. Two ribavirin-resistant mutants, RVRp13 and RVRp22, emerged from serial passages in the presence of 0.1 and 0.2 mM ribavirin, respectively. The genetic stability of these resistant mutants was evaluated in MARC-145 cells and compared with VR2332. As expected, the ribavirin-resistant mutants exhibited higher genetic stability compared to their parental virus.

Conclusions

In summary, ribavirin and 5-fluorouracil effectively suppressed PRRSV replication in MARC-145 cells. However, ribavirin-resistant mutants emerged when treated with low concentrations (≤0.2 mM) of ribavirin, and those mutants were genetically more stable during serial passages in cell culture.

Improving the effectiveness of (-)-epigallocatechin gallate (EGCG) against rabbit atherosclerosis by EGCG-loaded nanoparticles prepared from chitosan and polyaspartic acid

(-)-Epigallocatechin gallate (EGCG) is the major bioactive compound in green tea. Its effect is limited by the harsh environment of the gastrointestinal tract. The present study investigates how the effectiveness of EGCG is influenced by its encapsulation into self-assembled nanoparticles of chitosan (CS) and aspartic acid (PAA). Blank nanoparticles with a mean diameter of ca. 93 nm were prepared from 30-50 kDa PAA and 3-5 kDa CS with a mass rate of 1:1. EGCG was loaded in the nanoparticles to yield EGCG-CS-PAA nanoparticles with an average diameter of 102 nm, which were pH-responsive and demonstrated different EGCG release profiles in simulated gastrointestinal tract media. The average ratio (%) of lipid deposition for EGCG-CS-PAA nanoparticles administered orally to rabbits was 16.9 ± 5.8%, which was close to that of oral simvastatin (15.6 ± 4.1%). Orally administered EGCG alone yielded an average ratio of lipid deposit area of 42.1 ± 4.0%, whereas this value was 65.3 ± 10.8% for the blank nanoparticles. The effectiveness of EGCG against rabbit atherosclerosis was significantly improved by incorporating EGCG into the nanoformulation.

Porcine epidemic diarrhea virus induces caspase-independent apoptosis through activation of mitochondrial apoptosis-inducing factor

The present study sought to investigate whether porcine epidemic diarrhea virus (PEDV) induces apoptosis and to elucidate the mechanisms associated with apoptotic cell death after PEDV infection. PEDV-infected cells showed evidence of apoptosis in vitro and in vivo. However, experimental data indicated that the caspase cascade is not involved in PEDV-induced apoptotic cell death. Interestingly, mitochondrial apoptosis-inducing factor (AIF) was found to translocate to the nucleus during PEDV infection, and AIF relocalization was completely abrogated by the presence of cyclosporin A (CsA), an inhibitor of cyclophilin D (CypD) that is an essential component of the mitochondrial permeabilization transition pore (mPTP) complex. CsA treatment resulted in significant inhibition of PEDV-triggered apoptosis and suppressed PEDV replication. Furthermore, direct inhibition of AIF strongly impaired PEDV infection and virus-induced apoptosis. Altogether, our results indicate that a caspase-independent mitochondrial AIF-mediated pathway plays a central role in PEDV-induced apoptosis to facilitate viral replication and pathogenesis.

Actinobacillus pleuropneumoniae possesses an antiviral activity against porcine reproductive and respiratory syndrome virus

Pigs are often colonized by more than one bacterial and/or viral species during respiratory tract infections. This phenomenon is known as the porcine respiratory disease complex (PRDC). Actinobacillus pleuropneumoniae (App) and porcine reproductive and respiratory syndrome virus (PRRSV) are pathogens that are frequently involved in PRDC. The main objective of this project was to study the in vitro interactions between these two pathogens and the host cells in the context of mixed infections. To fulfill this objective, PRRSV permissive cell lines such as MARC-145, SJPL, and porcine alveolar macrophages (PAM) were used. A pre-infection with PRRSV was performed at 0.5 multiplicity of infection (MOI) followed by an infection with App at 10 MOI. Bacterial adherence and cell death were compared. Results showed that PRRSV pre-infection did not affect bacterial adherence to the cells. PRRSV and App co-infection produced an additive cytotoxicity effect. Interestingly, a pre-infection of SJPL and PAM cells with App blocked completely PRRSV infection. Incubation of SJPL and PAM cells with an App cell-free culture supernatant is also sufficient to significantly block PRRSV infection. This antiviral activity is not due to LPS but rather by small molecular weight, heat-resistant App metabolites (<1 kDa). The antiviral activity was also observed in SJPL cells infected with swine influenza virus but to a much lower extent compared to PRRSV. More importantly, the PRRSV antiviral activity of App was also seen with PAM, the cells targeted by the virus in vivo during infection in pigs. The antiviral activity might be due, at least in part, to the production of interferon γ. The use of in vitro experimental models to study viral and bacterial co-infections will lead to a better understanding of the interactions between pathogens and their host cells, and could allow the development of novel prophylactic and therapeutic tools.

In vitro evaluation of the antiviral activity of the synthetic epigallocatechin gallate analog-epigallocatechin gallate (EGCG) palmitate against porcine reproductive and respiratory syndrome virus

In this study, epigallocatechin gallate (EGCG) palmitate was synthesized and its anti-porcine reproductive and respiratory syndrome virus (PRRSV) activity was studied. Specifically, EGCG palmitate was evaluated for its ability to inhibit PRRSV infection in MARC-145 cells when administered as pre-, post-, or co-treatment. EGCG and ribavirin were used as controls. The results showed that a 50% cytotoxic concentration (CC50) of EGCG, EGCG palmitate, and ribavirin was achieved at 2,359.71, 431.42, and 94.06 μM, respectively. All three drugs inhibited PRRSV in a dose-dependent manner regardless of the treatment protocol. EGCG palmitate exhibited higher cytotoxicity than EGCG, but lower cytotoxicity than ribavirin. EGCG palmitate anti-PRRSV activity was significantly higher than that of EGCG and ribavirin, both as pre-treatment and post-treatment. Under the former conditions and a tissue culture infectious dose of 10 and 100, the selectivity index (SI) of EGCG palmitate in the inhibition of PRRSV was 3.8 and 2.9 times higher than that of ribavirin when administered as a pre-treatment, while the SI of EGCG palmitate in the inhibition of PRRSV was 3.0 and 1.9 times higher than ribavirin when administered as a post-treatment. Therefore, EGCG palmitate is potentially effective as an anti-PRRSV agent and thus of interest to the pharmaceutical industry.

Yeast-based assays for the high-throughput screening of inhibitors of coronavirus RNA cap guanine-N7-methyltransferase

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A yeast-based system for screening of coronavirus N7-MTases inhibitors was developed.

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Sinefungin is not an ideal antiviral inhibitor.

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Three natural extracts were observed to specifically inhibit the N7-MTases of coronavirus.

The 5′-cap structure is a distinct feature of eukaryotic mRNAs and is important for RNA stability and protein translation by providing a molecular signature for the distinction of self or non-self mRNA. Eukaryotic viruses generally modify the 5′-end of their RNAs to mimic the cellular mRNA structure, thereby facilitating viral replication in host cells. However, the molecular organization and biochemical mechanisms of the viral capping apparatus typically differ from its cellular counterpart, which makes viral capping enzymes attractive targets for drug discovery. Our previous work showed that SARS coronavirus (SARS-CoV) non-structural protein 14 represents a structurally novel and unique guanine-N7-methyltransferase (N7-MTase) that is able to functionally complement yeast cellular N7-MTase. In the present study, we developed a yeast-based system for identifying and screening inhibitors against coronavirus N7-MTase using both 96-well and 384-well microtiter plates. The MTase inhibitors previously identified by in vitro biochemical assays were tested, and some, such as sinefungin, effectively suppressed N7-MTase in the yeast system. However, other compounds, such as ATA and AdoHcy, did not exert an inhibitory effect within a cellular context. These results validated the yeast assay system for inhibitor screening yet also demonstrated the difference between cell-based and in vitro biochemical assays. The yeast system was applied to the screening of 3000 natural product extracts, and three were observed to more potently inhibit the activity of coronavirus than human N7-MTase.

Antiviral activity and underlying molecular mechanisms of Matrine against porcine reproductive and respiratory syndrome virus in vitro

Porcine reproductive and respiratory syndrome (PRRS), caused by porcine reproductive and respiratory syndrome virus (PRRSV), is an acute infectious disease. The prevalence of PRRS has made swine industry suffered huge financial losses. Matrine, a natural compound, has been demonstrated to possess anti-PRRSV activity in Marc-145 cells. However, the underlying molecular mechanisms were still unknown. The main objective of our study was to discuss the effect of Matrine on PRRSV N protein expression and PRRSV induced apoptosis. Indirect immunofluorescence assay (IFA) and Western blot were used to assess the effect of Matrine on N protein expression. Apoptosis was analyzed by fluorescence staining. In addition, the effect of Matrine on caspase-3 activation was investigated by Western blot. Indirect immunofluorescence assay and Western blot analysis demonstrated that Matrine could inhibit N protein expression in Marc-145 cells. And Matrine was found to be able to impair PRRSV-induced apoptosis by inhibiting caspase-3 activation.

Extinction of hepatitis C virus by ribavirin in hepatoma cells involves lethal mutagenesis

Lethal mutagenesis, or virus extinction produced by enhanced mutation rates, is under investigation as an antiviral strategy that aims at counteracting the adaptive capacity of viral quasispecies, and avoiding selection of antiviral-escape mutants. To explore lethal mutagenesis of hepatitis C virus (HCV), it is important to establish whether ribavirin, the purine nucleoside analogue used in anti-HCV therapy, acts as a mutagenic agent during virus replication in cell culture. Here we report the effect of ribavirin during serial passages of HCV in human hepatoma Huh-7.5 cells, regarding viral progeny production and complexity of mutant spectra. Ribavirin produced an increase of mutant spectrum complexity and of the transition types associated with ribavirin mutagenesis, resulting in HCV extinction. Ribavirin-mediated depletion of intracellular GTP was not the major contributory factor to mutagenesis since mycophenolic acid evoked a similar decrease in GTP without an increase in mutant spectrum complexity. The intracellular concentration of the other nucleoside-triphosphates was elevated as a result of ribavirin treatment. Mycophenolic acid extinguished HCV without an intervening mutagenic activity. Ribavirin-mediated, but not mycophenolic acid-mediated, extinction of HCV occurred via a decrease of specific infectivity, a feature typical of lethal mutagenesis. We discuss some possibilities to explain disparate results on ribavirin mutagenesis of HCV.

In vitro antiviral activity and underlying molecular mechanisms of dipotassium glycyrrhetate against porcine reproductive and respiratory syndrome virus

BACKGROUND

Porcine reproductive and respiratory syndrome virus (PRRSV) has caused large economic losses in the swine industry. Currently, there is no effective way to prevent PRRSV infection. In this study, we investigated the inhibitory effect of dipotassium glycyrrhetate (DG), a derivative of glycyrrhetinic acid, on PRRSV infection ability.

METHODS

The cytotoxicity of DG was measured by MTT assay, and the effects of DG on PRRSV N gene/protein were investigated using real-time PCR, western blot and immunofluorescence assay. In addition, the effect of DG on cell apoptosis was analysed by fluorescence staining.

RESULTS

Our results indicated that DG could effectively inhibit virus replication and N gene expression in MARC-145 cells infected with PRRSV. When the infected cells received DG, the numbers of apoptotic cells were decreased, and the cleaved caspase-3 contents were decreased dramatically.

CONCLUSIONS

Our study demonstrates that DG could effectively inhibit the PRRS virus via multiple pathways including inhibition of virus replication and N gene expression and reduction of apoptotic cells. DG can serve as a potential chemical for PRRSV prevention and control.