A new coumarin derivative plays a role in rhabdoviral clearance by interfering glycoprotein function during the early stage of viral infection

Kaempferol is a novel antiviral agent against channel catfish virus infection through blocking viral attachment and penetration in vitro

Channel catfish virus (CCV, Ictalurid herpesvirus 1) is the causative pathogen of channel catfish virus disease, which has caused high mortality and substantial economic losses in the catfish aquaculture industry. Due to the lack of licensed prophylactic vaccines and therapeutic drugs, the prevention and control of CCV infection seem to remain stagnant. Active compounds from medicinal plants offer eligible sources of pharmaceuticals and lead drugs to fight against endemic and pandemic diseases and exhibit excellent effect against viral infection. In this study, we evaluated the antiviral ability of 12 natural compounds against CCV with cell models in vitro and found kaempferol exhibited the strongest inhibitory compound against CCV infection among all the tested compounds. Correspondingly, kaempferol decreased transcription levels of viral genes and the synthesis of viral proteins, as well as reduced proliferation and release of viral progeny, the severity of the CPE induced by CCV in a dose-dependent manner, based on quantitative real-time PCR (RT-qPCR), western blotting, viral cytopathic effects (CPE) and viral titer assessment. Moreover, time-of-drug-addition assays, virus attachment, and penetration assays revealed that kaempferol exerted anti-CCV activity probably by blocking attachment and internalization of the viral entry process. Altogether, the present results indicated that kaempferol may be a promising candidate antiviral agent against CCV infection, which shed light on the development of a novel and potent treatment for fish herpesvirus infection.

Infection of epithelioma papulosum cyprini (EPC) cells with spring viremia of carp virus (SVCV) induces autophagy and apoptosis through endoplasmic reticulum stress

Spring viremia of carp virus (SVCV) is a lethal freshwater pathogen of cyprinid fish that has caused significant economic losses to aquaculture. To reduce the economic losses caused by SVCV, its pathogenic mechanism needs to be studied more thoroughly. Here, we report for the first time that SVCV infection of Epithelioma papulosum cyprini (EPC) cells can induce cellular autophagy and apoptosis through endoplasmic reticulum stress. The presence of autophagic vesicles in infected EPC cells was shown by transmission electron microscopy. Quantitative fluorescence PCR and Western blot results showed that p62 mRNA expression was decreased, and the expression of Beclin1 and LC3 mRNA was increased. The p62 protein was decreased, and the Beclin1 protein and LC3 were increased in the endoplasmic reticulum stress activation state. To further clarify the mode of death of SVCV-infected EPC cells, we examined caspase3, caspase9, BCL-2, and Bax mRNA, which showed that they were all increased. Apoptosis of SVCV-infected cells increased upon activation of endoplasmic reticulum stress. Our results suggest that endoplasmic reticulum stress can regulate SVCV infection-induced autophagy and apoptosis. The results of this study provide theoretical data for the pathogenesis of SVCV and lay the foundation for future drug development and vaccine construction.

Antiviral foods in the battle against viral infections: Understanding the molecular mechanism

Viruses produce a variety of illnesses, which may also cause acute respiratory syndrome. All viral infections, including COVID-19, are associated with the strength of the immune system. Till now, traditional medicine or vaccines for most viral diseases have not been effective. Antiviral and immune-boosting diets may provide defense against viral diseases by lowering the risk of infection and assisting rapid recovery. The purpose of this review was to gather, analyze, and present data based on scientific evidence in order to provide an overview of the mechanistic insights of antiviral bioactive metabolites. We have covered a wide range of food with antiviral properties in this review, along with their potential mechanism of action against viral infections. Additionally, the opportunities and challenges of using antiviral food have been critically reviewed. Bioactive plant compounds, not only help in maintaining the body's normal physiological mechanism and good health but are also essential for improving the body's immunity and therefore can be effective against viral diseases. These agents fight viral diseases either by incorporating the body's defense mechanism or by enhancing the cell's immune system. Regular intake of antiviral foods may prevent future pandemic and consumption of these antiviral agents with traditional medicine may reduce the severity of viral diseases. Therefore, the synergistic effect of antiviral foods and medication needs to be investigated.

4'-(8-(4-Methylimidazole)-octyloxy)-arctigenin: The first inhibitor of fish rhabdovirus glycoprotein

Spring viraemia of carp virus (SVCV), a highly pathogenic rhabdovirus, could cause spring viraemia of carp (SVC) with up to 90% lethality. Like other rhabdoviruses, the entry of SVCV into susceptible cells was mediated by a single envelope glycoprotein G. Specific inhibitors targeting the glycoprotein were the most effective means to alleviate the epidemic. The programs including SWISS-MODEL, I-TASSER, Phyre2 and AlphaFold2 were used to build a three-dimensional structural model of glycoprotein. The structural comparison between SVCV-G and homology protein VSV-G revealed that the SVCV glycoprotein ectodomain (residues 19 to 466) folded into four distinct domains. Based on the potential small molecule binding sites on glycoprotein surfaces, virtual screening of the anti-SVCV drug libraries was performed using Autodock software and 4'-(8-(4-Methylimidazole)-octyloxy)-arctigenin (MOA) with a high binding affinity was identified. The solubility enhancer tags including trigger factor and maltose binding protein were fused with the ectodomain of glycoprotein, and the target protein with a purity of about 90% was successfully obtained. The interaction confirmation tests revealed that the fluorescence intensity of a characteristic peak induced by the endogenous chromophores in glycoprotein was decreased with the addition of MOA, indicating changes in the microenvironment of glycoprotein. Moreover, the interaction could cause a slight conformational change in glycoprotein, as shown by the content of β-turn, β-folding, and random coil of protein all increased with the decrease of α-helix content after the addition of MOA compound. These results demonstrated that MOA could act as a novel drug against fish rhabdovirus via direct targeting of glycoprotein.

Structure of the Spring Viraemia of Carp Virus Ribonucleoprotein Complex Reveals Its Assembly Mechanism and Application in Antiviral Drug Screening

Spring viremia of carp virus (SVCV) is a highly pathogenic Vesiculovirus infecting the common carp, yet neither a vaccine nor effective therapies are available to treat spring viremia of carp (SVC). Like all negative-sense viruses, SVCV contains an RNA genome that is encapsidated by the nucleoprotein (N) in the form of a ribonucleoprotein (RNP) complex, which serves as the template for viral replication and transcription. Here, the three-dimensional (3D) structure of SVCV RNP was resolved through cryo-electron microscopy (cryo-EM) at a resolution of 3.7 Å. RNP assembly was stabilized by N and C loops; RNA was wrapped in the groove between the N and C lobes with 9 nt nucleotide per protomer. Combined with mutational analysis, our results elucidated the mechanism of RNP formation. The RNA binding groove of SVCV N was used as a target for drug virtual screening, and it was found suramin had a good antiviral effect. This study provided insights into RNP assembly, and anti-SVCV drug screening was performed on the basis of this structure, providing a theoretical basis and efficient drug screening method for the prevention and treatment of SVC. IMPORTANCE Aquaculture accounts for about 70% of global aquatic products, and viral diseases severely harm the development of aquaculture industry. Spring viremia of carp virus (SVCV) is the pathogen causing highly contagious spring viremia of carp (SVC) disease in cyprinids, especially common carp (Cyprinus carpio), yet neither a vaccine nor effective therapies are available to treat this disease. In this study, we have elucidated the mechanism of SVCV ribonucleoprotein complex (RNP) formation by resolving the 3D structure of SVCV RNP and screened antiviral drugs based on the structure. It is found that suramin could competitively bind to the RNA binding groove and has good antiviral effects both in vivo and in vitro. Our study provides a template for rational drug discovery efforts to treat and prevent SVCV infections.

Inhibition of the largemouth bass virus replication by piperine demonstrates potential application in aquaculture

Largemouth bass virus (LMBV) is a systemic viral pathogen that can cause high mortality rates in cultivated largemouth bass. However, no treatment is currently approved. Therapeutic strategies against LMBV infection are urgently needed. In this study, we investigated the antiviral activity of piperine against LMBV in vitro and in vivo. In vitro antiviral activity assay showed that 210.28 μM piperine significantly decreased LMBV major capsid protein (MCP) gene expression in epithelioma papulosum cyprinid (EPC) cells by a maximum inhibitory rate of >95%. Piperine treatment inhibited LMBV replication in a dose-dependent manner, with the half-maximal activity (IC₅₀ ) of 34.61 μM. Moreover, piperine significantly decreased the viral titers and cytopathic effects (CPE), contributing to the protection of infected cells. With regard to the steps of piperine affecting the life cycle of viruses, piperine had a direct inactivating effect on LMBV. During the virus adsorption phase, piperine prevented the adsorption of LMBV to EPC cells. Furthermore, piperine played an antiviral role mainly in the later stages of viral infection (4-8 h). To further evaluate the antiviral activity of piperine against LMBV in vivo, largemouth bass as a model organism was carried out in relevant experiments. Intraperitoneal injection of piperine (25 mg/kg) effectively improved the survival rate of LMBV-infected largemouth bass by 20%. In addition, RT-qPCR results of viral replication in liver, spleen, kidney, gill and swim bladder tissues showed that piperine significantly inhibited LMBV replication in vivo, thus protecting largemouth bass from LMBV-induced death. Together, our results suggested that piperine is a therapeutic and preventative agent against LMBV infection.

Immunostimulants for shrimp aquaculture: paving pathway towards shrimp sustainability

At present, food security is a matter of debate of global magnitude and fulfilling the feeding requirement of > 8 billion human populations by 2030 is one of the major concerns of the globe. Aquaculture plays a significant role to meet the global food requirement. Shrimp species such as Litopenaeus vannamei, Penaeus monodon, and Macrobrachium rosenbergii are among the most popular food commodities worldwide. As per Global Outlook for Aquaculture Leadership survey, disease outbreaks have been a matter of concern from the past many decades regarding the shrimp aquaculture production. Among the past disease outbreaks, white spot disease caused by the white spot syndrome virus is considered to be one of the most devastating ones that caused colossal losses to the shrimp industry. Since the virus is highly contagious, it spreads gregariously among the shrimp population; hence, practicing proper sanitization practices is crucial in order to have disease-free shrimps. Additionally, in order to control the disease, antibiotics were used that further leads to bioaccumulation and biomagnification of antibiotics in several food webs. The bioaccumulation of the toxic residues in the food webs further adversely affected human too. Recently, immunostimulants/antivirals were used as an alternative to antibiotics. They were found to enhance the immune system of shrimps in eco-friendly manner. In context to this, the present paper presents a critical review on the immunostimulants available from plants, animals, and chemicals against WSSV in shrimps. Looking into this scenario, maintaining proper sanitation procedures in conjunction with the employment of immunostimulants may be a viable approach for preserving shrimp aquaculture across the globe.

Taxifolin Inhibits WSSV Infection and Transmission by Increasing the Innate Immune Response in Litopenaeus vannamei

An outbreak of white spot syndrome virus (WSSV) can hit shrimp culture with a devastating blow, and there are no suitable measures to prevent infection with the virus. In this study, the activity of active molecules from Chinese herbs against WSSV was evaluated and screened. Taxifolin had the highest rate (84%) of inhibition of the WSSV infection. The viral infectivity and genome copy number were reduced by 41% when WSSV virion was pretreated with taxifolin prior to shrimp infection. A continuous exchange of taxifolin significantly reduced the mortality of shrimp infected with WSSV. Due to the WSSV virion infectivity being affected by taxifolin, the horizontal transmission of the virus was blocked with an inhibition rate of up to 30%, which would further reduce the cost of a viral outbreak. Additionally, the viral genome copy number was also reduced by up to 63% in shrimp preincubated in taxifolin for 8 h. There may be a connection to the enhancement of innate immunity in shrimp that resulted in a 15% reduction in mortality for taxifolin-fed shrimp after the WSSV challenge. After dietary supplementation with taxifolin, the resistance of larvae to WSSV was improved, indicating that taxifolin may be a potential immunostimulant for shrimp to prevent WSD. Therefore, the results indicate that taxifolin has application potential for blocking a WSSV outbreak and reducing the loss of shrimp culture.

Amantadine, a promising therapeutic agent against viral encephalopathy and retinopathy

Outbreaks of viral encephalopathy and retinopathy (VER) in marine and freshwater species severely devastate the aquaculture worldwide. The causative agent of VER is nervous necrosis virus (NNV), which mainly infects the early developmental stages of fish, limiting the effectiveness of vaccines. To counter this case, the anti-NNV potentials of nine drugs with broad-spectrum antiviral activity were explored using ribavirin as a positive drug. Toxicity of the selected drugs to SSN-1 cells and grouper was firstly evaluated to determine the safety concentrations. For screening in vitro, amantadine and oseltamivir phosphate can relieve the cytopathic effects and inhibit NNV replication with the 90% inhibitory concentrations (IC₉₀ ) of 38.74 and 106.75 mg/L, respectively. Amantadine has a stronger anti-NNV activity than ribavirin at the with- and post-NNV infection stages, indicating that it is a potential therapeutic agent against VER by acting directly on NNV. Similarly, amantadine also has a strong anti-NNV activity in vivo with the IC₉₀ of 27.91 mg/L at the 7 days post-infection, while that was 73.25 mg/L for ribavirin. Following exposure to amantadine (40 mg/L) and ribavirin (100 mg/L) for 7 days, the survival rates of NNV-infected grouper were increased to 44% and 39%, respectively. The maximum amantadine content (11.88 mg/Kg) in grouper brain was reached following exposure for 24 hr, and amantadine can be quickly excreted from fish, reducing the risk of drug residue. Results so far indicated that amantadine is a promising therapeutic agent against NNV in aquaculture, providing an effective strategy for VER control at the early developmental stages of fish.

Screening of potential spike glycoprotein / ACE2 dual antagonists against COVID-19 in silico molecular docking

The novel coronavirus disease has spread rapidly and caused sustained pressure on economic and medical resources to many countries. Vaccines and effective drugs are needed to fight against the epidemic. Traditional Chinese Medicine (TCM) plays an important and effective role in the treatment of COVID-19. Therefore, the active components of TCM are potential structural basis for the discovery of antiviral drugs. Through screening by molecular docking, Oleanolic acid, Tryptanthrin, Chrysophanol and Rhein were found to have better spike protein and ACE2 inhibitory activity, which could block the invasion and recognition of SARS-CoV-2 at the same time, should be investigated as antiviral candidates.

Small Molecule Inhibitors of White Spot Syndrome Virus: Promise in Shrimp Seedling Culture

Rapid production of prawn (Litopenaeus vannamei) under artificial pressure can result in a series of obvious challenges and is vulnerable to serious losses related to aquatic environmental issues and the unrestrained outbreak of white spot syndrome (WSS). However, to date, there are no therapeutic strategies to contain the spread of the virus. Here, we synthesized 27 coumarin derivatives and evaluated their anti-white spot syndrome virus (WSSV) activity in L. vannamei larvae. We demonstrated that electron-withdrawing and electron-giving substituent groups play an important role in reducing toxicity and WSSV replication, respectively. Two coumarin C2 (2-amino-5-oxo-4-(p-tolyl)-4H,5H-pyrano[3,2-c]chromene-3-carbonitrile) and C7 (2-amino-4-(4-chlorophenyl)-5-oxo-4H,5H-pyrano[3,2-c]chromene-3-carbonitrile) were regarded as the most promising anti-WSSV compounds with maximum antiviral response <5% and median effective concentration <10 mg/L. The mortality of WSSV-infected larvae decreased by more than 60% after exposure to C2 and C7. With continuous immersion of C2 and C7 exchange, the mortality further decreased to 40% at 120 h. Additionally, C2 and C7 are the relatively stable in aquacultural water, making these agents suitable for use in inhibiting WSSV horizontal transmission in static aquaculture systems. These results showed the marked advantages of using C2 and C7 in the shrimp industry, and suggest that they hold potential for the treatment and prevention of WSSV infection in shrimp seedling culture.

A novel antiviral coumarin derivative as a potential agent against WSSV infection in shrimp seedling culture

White spot syndrome virus (WSSV), a double-stranded DNA virus that infects crustaceans, is the most serious viral pathogen affecting shrimp farming worldwide. To reduce the economic losses caused by WSSV, we screened a novel coumarin derivative from a small molecule drug library, N-(4-((4-(((2-oxo-2H-chromen-7-yl)oxy)methyl)-1H-1,2,3-triazol-1-yl)sulfonyl)phenyl)acetamide (N2905), to evaluate its anti-WSSV effects in vivo. We determined that compound N2905, up to a concentration of 20 mg/L, significantly decreased the number of WSSV copies in Litopenaeus vannamei post-larvae, with a maximum inhibitory rate of > 90 %, and increased the survival rate of WSSV-infected post-larvae. Pre-treatment and post-treatment assays indicated that N2905 could treat, but not prevent, WSSV infections. When WSSV was preincubated with N2905 for 1-4 h, the incidence of viral infections was significantly reduced and survival time of post-larvae extended to 120 h. A stability study of N2905 provided a reference for its practical use. Considering the antiviral stability of N2905 in culture water within 2 d, continuous N2905 exchange was performed, showing a significant decrease in viral load at 120 h post-infection (hpi) and a 55 % increase in survival of WSSV-infected post-larvae. Overall, our study demonstrated the potential of N2905 as an antiviral agent.

A preliminary investigation on the mechanism of action of 4-(8-(2-ethylimidazole)octyloxy)-arctigenin against IHNV

Arctigenin derivatives form an elite class of naturally occurring compounds that possess promising antiviral therapeutic perspectives. In a previous study, we design and synthesize a arctigenin derivative, 4-(8-(2-ethylimidazole)octyloxy)-arctigenin (EOA), to evaluate its antiviral activity on infectious hematopoietic necrosis virus (IHNV). In this study, we find that the half maximal inhibitory concentrations (IC₅₀) of EOA on IHNV nucleoprotein (N), phosphoprotein (P), matrix protein (M), nonvirion protein (NV) and polymerase (L) mRNA expression is 0.92, 0.80, 0.98, 0.89 and 0.87 μM, respectively. Mechanistically, our results show that EOA do not damage the viral particles directly, indicating EOA does not possess antiviral activity by destroying virions. Viral binding assays reveal that EOA do not interfere with IHNV adsorption. Because rapamycin has been shown to exhibit anti-IHNV activity by inducing autophagy of epithelioma papulosum cyprini (EPC) cells, we further investigate the relationship between EOA and autophagy in EPC cells. Autophagy fluorescence detection shows that EPC cells have a strong autophagy body after being treated with derivative EOA. The electron microscopy results show that EOA could induce typical autophagosomes which are representative structures of autophagy activation. Moreover, the punctate accumulation of green fluorescence-tagged microtubule-associate protein 1 light chain 3 (LC3) and the protein conversion from LC3-I to LC3-II are respectively confirmed by confocal fluorescence microscopy and western blotting. Overall, these findings demonstrate that EOA plays an anti-IHNV role via inducing autophagy in EPC cells.

Phosphatidylinositol-3-kinase-Akt pathway in negative-stranded RNA virus infection: a minireview

The PI3K/Akt signalling pathway is a crucial signalling cascade that regulates transcription, protein translation, cell growth, proliferation, cell survival, and metabolism. During viral infection, viruses exploit a variety of cellular pathways, including the well-known PI3K/Akt signalling pathway. Conversely, cells rely on this pathway to stimulate an antiviral response. The PI3K/Akt pathway is manipulated by a number of viruses, including DNA and RNA viruses and retroviruses. The aim of this review is to provide up-to-date information about the role of the PI3K-Akt pathway in infection with members of five different families of negative-sense ssRNA viruses. This pathway is hijacked for viral entry, regulation of endocytosis, suppression of premature apoptosis, viral protein expression, and replication. Although less common, the PI3K/Akt pathway can be downregulated as an immunomodulatory strategy or as a mechanism for inducing autophagy. Moreover, the cell activates this pathway as an antiviral strategy for interferon and cytokine production, among other strategies. Here, we present new data concerning the role of this pathway in infection with the paramyxovirus Newcastle disease virus (NDV). Our data seem to indicate that NDV uses the PI3K/Akt pathway to delay cell death and increase cell survival as a means of improving its replication. The interference of negative-sense ssRNA viruses with this essential pathway might have implications for the development of antiviral therapies.

Evaluation on the antiviral effect of a hydroxycoumarin against infectious hematopoietic necrosis virus infection in vitro and in vivo

Infectious hematopoietic necrosis (IHN) caused by the viral pathogen infectious hematopoietic necrosis virus (IHNV) is a highly contagious disease of salmonid species, resulting in significant economic impact. The previous study showed a hydroxycoumarin derivative 7-[6-(2-methylimidazole) hexyloxy] coumarin (D5) significantly inhibited spring viraemia of carp virus (SVCV) infection, suggesting that D5 may be useful as a potential anti-IHNV agent. In this study, D5 at the concentration of up to 10 mg/L significantly inhibited IHNV replication in epithelioma papulosum cyprini (EPC) cells with a maximum inhibitory rate of >90%, maintained mitochondrial membrane potential (ΔΨm) levels, and decreased IHNV-induced apoptosis in virus-infected cells. As the consequence of protection on mitochondria, D5 enhanced antioxidant enzyme activities and decreased reactive oxygen species (ROS) to maintain the antioxidant-oxidant balance of IHNV-infected EPC cells. For in vivo study, D5 via intraperitoneal injection exhibited an anti-IHNV effect in the virus-infected fish by substantially enhancing the survival rate. Meanwhile, up-regulation of six interferon (IFN) related gene expressions demonstrated that D5 may activate IFN-related expressions for inhibiting IHNV replication during the early stage of viral infection, which is beneficial for the continuous antiviral action on controlling low viral loads in rainbow trout juvenile. Thus, D5 effective regulated IHNV-induced undesirable conditions to be an excellent potential therapeutic agent against IHNV infection.

Inhibition of a novel coumarin on an aquatic rhabdovirus by targeting the early stage of viral infection demonstrates potential application in aquaculture

Spring viremia of carp virus (SVCV) is one of the most serious pathogens in aquaculture, resulting in devastating damage in cyprinid. In this study, we designed and synthesized a novel coumarin derivative (C3007) for evaluating its in vitro and in vivo anti-SVCV effects. Here, we determined that up to 25 mg/L C3007 significantly decreased SVCV protein gene expression levels in EPC cells by a maximum inhibitory rate of >95%. When C3007 was preincubated with SVCV, infectivity was significantly inhibited in vitro in a time-dependent manner, with complete inhibition at 25 mg/L. For in vivo studies, C3007 exhibited an anti-SVCV effect by substantially enhancing the survival rate of virus-infected fish via intraperitoneal injection. Although the horizontal transmission of SVCV was hindered by C3007 in a static cohabitation challenge model, it was not completely blocked, showing that the viral loads in recipient fish were obviously reduced. Thus, C3007 could potentially be used as a therapeutic agent with great potential in aquatic systems and may also be suitable for applications in pond aquaculture settings against viral transmission. Additionally, the C3007-preincubated virus induced an antiviral immune response with high levels of IFN expression, suggesting that C3007 pre-treatment could be used in vaccine development.

Antiviral activity of anisomycin against spring viraemia of carp virus in epithelioma papulosum cyprini cells and zebrafish

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Anisomycin caused profound inhibition of SVCV replication in EPC cells.

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Anisomycin blocked morphological cell damage caused by SVCV replication.

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Anisomycin suppressed SVCV replication in vivo, resulting in a prolonged survival of infected zebrafish.

Spring viraemia of carp (SVC) caused by spring viraemia of carp virus (SVCV) is an acute and highly lethal viral disease of cyprinid fish. However, effective therapy for SVC is still scarce until now. Here we evaluated the inhibition of anisomycin (Ani), a metabolite produced by Streptomyces griseolus, on the replication of SVCV in vitro and in vivo. Our results demonstrated that Ani could suppress SVCV replication with the maximum inhibitory rate > 95% in epithelioma papulosum cyprini (EPC) cells. And the half maximal inhibitory concentrations (IC₅₀) of Ani on SVCV glycoprotein (G), nucleoprotein (N) and phosphoprotein mRNA expressions were 21.79, 13.13 and 12.24 nM, respectively. Besides, Ani decreased SVCV-induced cytopathic effects and nucleus damages. As expected, Ani also showed a strong anti-SVCV activity in vivo, as indicated by inhibiting viral gene expression and increasing the survival rate of zebrafish. Intraperitoneal injection of Ani increased the survival rate of zebrafish by 30% and markedly inhibited the expressions of G and N mRNA by > 60% in kidney and spleen at day 1 and day 4 post-infection. Results so far suggest that Ani as a powerful agent against SVCV can be applied to the control of SVC in aquaculture.