Evaluation on the antiviral activity of ribavirin against infectious hematopoietic necrosis virus in epithelioma papulosum cyprini cells

MK-0608 inhibits in vitro and in vivo RNA replication of infectious pancreatic necrosis virus

Infectious pancreatic necrosis virus (IPNV) is an important pathogen that is threatening the worldwide salmon and trout industry. But there is no therapeutic drug available for now. In this study, we demonstrate that MK-0608 is highly efficient against IPNV and low cytotoxic, with a 50 % effective concentration (EC50) of 0.20 μM and selectivity index (SI) of about 268. Time of addition assay illustrated that MK-0608 targeted the early stage of IPNV life cycle. Furthermore, we found that MK-0608 blocked IPNV attachment on the premise of sufficient pre-incubation time but MK-0608 did not influence viral internalization and release. MK-0608 could inhibit IPNV genome synthesis, and combination with ribavirin enhanced the inhibition effect, which might be functional via binding to IPNV RNA dependent RNA polymerase (RdRp), which was predicted by using molecular docking methods. In vivo test showed that IPNV was extremely suppressed in the rainbow trout (Oncorhynchus mykiss) with one single dose of MK-0608, and the higher dosage of 50 mg/kg could cause 3 log decrease of IPNV loads in fish tissues.

Effects on viral suppression and the early-immune expression of ribavirin against spring viremia of carp virus in vitro

Spring viremia of carp virus (SVCV) is a globally distributed virus that causes severe clinical symptoms and high mortality in fish belonging to the families Cyprinidae and Siluridae. To protect the host against viral infection, understanding the relatedness between viral susceptibility and antiviral mechanisms must be crucial. Thus, we evaluated the viral suppression efficacy of ribavirin by measuring the transcription levels of viral and immune genes in vitro. The results showed that following ribavirin treatment after SVCV infection (MOI 0.1), ribavirin inhibited SVCV replication in epithelioma papulosum cyprini (EPC) cells and completely inhibited viral gene (G and N) expression at concentrations above 10 μg/mL at 48 h post-infection. Ribavirin does not directly damage SVCV particles but inhibits early viral replication. In the absence of SVCV infection, the immunological dynamics triggered by ribavirin resulted in upregulated pattern recognition receptors and proinflammatory cytokine-related genes (i.e., PI3K, MYD88, IRAK1, RIG-І, MAVS, Mx1, TNF-α, and NF-κB). Furthermore, EPC cells treated with ribavirin following SVCV infection showed upregulation of PI3K, MYD88, IRAK1, RIG-І, TNF-α, and NF-κB genes within 24 h post-SVCV infection, suggesting that ribavirin positively inhibits the SVCV infection in vitro.

A therapeutic agent of ursolic acid demonstrates potential application in aquaculture

Micropterus salmoides rhabdovirus (MSRV) has a high mortality rate and causes huge economic losses to the aquaculture industry. In this study, we identified that ursolic acid (UA) had antiviral efficacy against MSRV in vitro and in vivo. The results showed that UA inhibited MSRV replication in grass carp ovary (GCO) cells with a half-maximal inhibitory concentration (IC50) of 5.55 μM, reduced viral titers and decreased cytopathic effects (CPE). Mechanistically, UA does not directly damage viral particles. On the other hand, UA inhibits MSRV replication by altering viral binding and release. Furthermore, pre- and post-treatment assays revealed that UA had preventive and therapeutic effects. For in vivo studies, UA could enhance the survival rate of MSRV-infected largemouth bass. Similarly, UA reduced the viral load of MSRV in the heart, spleen and brain at 3, 5 and 7 d post-infection. In conclusion, UA is an effective inhibitor of rhabdovirus in aquaculture.

Antiviral Activity of Ribavirin against Tilapia tilapinevirus in Fish Cells

The outbreak of the novel Tilapia tilapinevirus or Tilapia lake virus (TiLV) is having a severe economic impact on global tilapia aquaculture. Effective treatments and vaccines for TiLV are lacking. In this study, we demonstrated the antiviral activity of ribavirin against TiLV in E-11 cells. Our findings revealed that at concentrations above 100 μg/mL, ribavirin efficiently attenuates the cytopathic effect of the TiLV infection in fish cells. When administered in a dose-dependent manner, ribavirin significantly improved cell survival compared to the untreated control cells. Further investigation revealed that the cells exposed to ribavirin and TiLV had a lower viral load (p < 0.05) than the untreated cells. However, at concentrations above 1000 μg/mL, ribavirin led to cell toxicity. Taken together, our results demonstrate the efficacy of this antiviral drug against TiLV and could be a useful tool for future research on the pathogenesis and replication mechanism of TiLV as well as other piscine viruses.

Acyclovir inhibits white spot syndrome virus replication in crayfish Procambarus clarkii

White spot syndrome virus (WSSV) is a fatal pathogen threatening global crustacean industry with no commercially available drugs to control WSSV. To address the urgent need for finding effective antiviral agents against WSSV, we examined the anti-WSSV activities of 11 common antiviral agents in crayfish Procambarus clarkia. The results showed that acyclovir displayed the highest inhibition on WSSV replication in vivo (92.59%, 50 mg/kg). Acyclovir repressed WSSV proliferation followed a dose-dependent fashion and pre- or post-treatment of acyclovir exerted strong inhibition on the viral loads. Further, we observed a markedly reduced expression levels of WSSV genes (immediate-early IE gene ie1, DNA polymerase gene DNApol and envelope protein gene Vp28) that are crucial in viral life cycle with the acyclovir treatment during the early infection. Meantime, we also found a significantly increased expressions of anti-oxidative as well as apoptosis related genes, suggesting that acyclovir could effectively suppress WSSV replication in vivo. Finally, acyclovir treatment could significantly improve the survival rate of WSSV-challenged crayfish by 56%. Taken together, acyclovir has the potential to be developed as a promising preventive or therapeutic agent against WSSV infection, and this finding may provide a reference for rapid discovery anti-WSSV agent in crustacean aquaculture.

Synthesis and biological evaluation of novel coumarin derivatives in rhabdoviral clearance

Diseases caused by rhabdoviruses have had a huge impact on the productive lives of the entire human population. The main problem is the lack of drugs for the treatment of this family of viruses. Infectious hematopoietic necrosis virus (IHNV), the causative agent of IHN, is a typical rhabdovirus which has caused huge losses to the salmonid industry. Therefore, in this study, IHNV was studied as a model to evaluate the antiviral activity of 35 novel coumarin derivatives. Coumarin A9 was specifically selected for further validation studies upon comparing the half maximum inhibitory concentration (IC₅₀) of four screened candidate derivatives in epithelioma papulosum cyprinid (EPC) cells, as it exhibited an IC₅₀ value of 2.96 μM against IHNV. The data revealed that A9 treatment significantly suppressed the virus-induced cytopathic effect (CPE) in EPC cells. In addition, A9 showed IC₅₀ values of 1.68 and 2.12 μM for two other rhabdoviruses, spring viremia of carp virus and micropterus salmoides rhabdovirus, respectively. Furthermore, our results suggest that A9 exerts antiviral activity, but not by destroying the virus particles and interfering with the adsorption of IHNV. Moreover, we found that A9 had an inhibitory effect on IHNV-induced apoptosis in EPC cells, as reflected by the protection against cell swelling, formation of apoptotic bodies, and loss of cell morphology and nuclear division. There was a 19.05 % reduction in the number of apoptotic cells in the A9 treatment group compared with that in the IHNV group. In addition, enzyme activity assays proved that A9 suppressed the expression of caspase 3, 8 and 9. These results suggested that A9 inhibit viral replication, to some extent, by blocking IHNV-induced apoptosis. In an in vivo study, A9 exhibited an anti-rhabdovirus effect in virus-infected fish by substantially enhancing the survival rate. Consistent with the above results, A9 repressed IHNV gene expression in virus-sensitive tissues (brain, kidney and spleen) in the early stages of virus infection. Importantly, the data showed that horizontal transmission of IHNV was reduced by A9 in a static cohabitation challenge model, especially in fish that underwent bath treatment, suggesting that A9 might be a suitable therapeutic agent for IHNV in aquaculture. Therefore, coumarin derivatives can be developed as antiviral agents against rhabdoviruses.

Ursolic acid from Prunella vulgaris L. efficiently inhibits IHNV infection in vitro and in vivo

Infectious hematopoietic necrosis virus (IHNV) is a fish viral pathogen that causes severe disease and huge economic losses in the salmonid aquaculture industry. However, anti-IHNV drugs currently are scarce. For the purpose of seeking out anti-IHNV drugs, the anti-IHNV activities of 32 medicinal plants were investigated by using epithelioma papulosum cyprini (EPC) cells. Among these plants, Prunella vulgaris L. (PVL) showed the strongest inhibition on IHNV replication with an inhibitory percentage of 99.3% at the concentration 100 mg/L. Further studies demonstrated that ursolic acid (UA), a major constituent of PVL, also showed a highly effective anti-IHNV activity. The half-maximal inhibitory concentration (IC50) at 72 h of UA on IHNV was 8.0 μM. Besides, UA could significantly decrease cytopathic effect (CPE) and the viral titer induced by IHNV in EPC cells. More importantly, UA also showed a strong anti-IHNV activity in vivo, as indicated by increasing the survival rate of rainbow trout and inhibiting viral gene expression. Intraperitoneal injection of UA increased the relative percentage of survival of rainbow trout by 18.9% and inhibited IHNV glycoprotein mRNA expression by > 90.0% in the spleen at the 1st-day post-infection. Altogether, UA was expected to be a therapeutic agent against IHNV infection in aquaculture.

Synthesis and antiviral activity of a new arctigenin derivative against IHNV in vitro and in vivo

Viral diseases in aquaculture were challenging because there are few preventative measures and/or treatments. Our previous study indicated that imidazole arctigenin derivatives possessed antiviral activities against infectious hematopoietic necrosis virus (IHNV). Based on the structure-activity relationship in that study, a new imidazole arctigenin derivative, 4-(8-(2-ethylimidazole)octyloxy)-arctigenin (EOA), was designed, synthesized and its anti-IHNV activity was evaluated. By comparing inhibitory concentration at half-maximal activity (IC₅₀), we found that EOA (IC₅₀ = 0.56 mg/L) possessed a higher antiviral activity than those imidazole arctigenin derivatives in our previous study. Besides, EOA could significantly decrease cytopathic effect (CPE) and viral titer induced by IHNV in epithelioma papulosum cyprinid (EPC) cells. In addition, EOA significantly inhibited apoptosis induced by IHNV in EPC cells. Further data verified that EOA inhibited IHNV replication in rainbow trout, with reducing 32.0% mortality of IHNV-infected fish. The results suggested that EOA was more stable with a prolonged inhibitory half-life in the early stage of virus infection (1-4 days). Consistent with above results, EOA repressed IHNV glycoprotein gene expression in virus sensitive tissues (kidney and spleen) in the early stage of virus infection. Moreover, histopathological evaluation showed that tissues from the spleen and kidney of fish infected with IHNV exhibited pathological changes. But there were no lesions in any of the tissues from the control group and EOA-treaten group. In accordance with the histopathological assay, EOA could elicited anti-inflammation response in non-viral infected rainbow trout by down-regulating the expression of cytokine genes (IL-8, IL-12p40, and TNF-α). Altogether, EOA was expected to be a therapeutic agent against IHNV infection in the field of aquaculture.