Gypenoside Inhibits Bovine Viral Diarrhea Virus Replication by Interfering with Viral Attachment and Internalization and Activating Apoptosis of Infected Cells

Bovine viral diarrhea virus (BVDV) causes a severe threat to the cattle industry due to ineffective control measures. Gypenoside is the primary component of Gynostemma pentaphyllum, which has potential medicinal value and has been widely applied as a food additive and herbal supplement. However, little is known about the antiviral effects of gypenoside. The present study aimed to explore the antiviral activities of gypenoside against BVDV infection. The inhibitory activity of gypenoside against BVDV was assessed by using virus titration and performing Western blotting, quantitative reverse transcription PCR (RT-qPCR), and immunofluorescence assays in MDBK cells. We found that gypenoside exhibited high anti-BVDV activity by interfering with the viral attachment to and internalization in cells. The study showed that BVDV infection inhibits apoptosis of infected cells from escaping the innate defense of host cells. Our data further demonstrated that gypenoside inhibited BVDV infection by electively activating the apoptosis of BVDV-infected cells for execution, as evidenced by the regulation of the expression of the apoptosis-related protein, promotion of caspase-3 activation, and display of positive TUNEL staining; no toxicity was observed in non-infected cells. Collectively, the data identified that gypenoside exerts an anti-BVDV-infection role by inhibiting viral attachment and internalization and selectively purging virally infected cells. Therefore, our study will contribute to the development of a novel prophylactic and therapeutic strategy against BVDV infection.

Quinolinecarboxamides Inhibit the Replication of the Bovine Viral Diarrhea Virus by Targeting a Hot Spot for the Inhibition of Pestivirus Replication in the RNA-Dependent RNA Polymerase

The bovine viral diarrhea virus (BVDV), a pestivirus from the family of Flaviviridae is ubiquitous and causes a range of clinical manifestations in livestock, mainly cattle. Two quinolinecarboxamide analogues were identified in a CPE-based screening effort, as selective inhibitors of the in vitro bovine viral diarrhea virus (BVDV) replication, i.e., TO505-6180/CSFCI (average EC₅₀ = 0.07 µM, SD = 0.02 µM, CC₅₀ > 100 µM) and TO502-2403/CSFCII (average EC₅₀ = 0.2 µM, SD = 0.06 µM, CC₅₀ > 100 µM). The initial antiviral activity observed for both hits against BVDV was corroborated by measuring the inhibitory effect on viral RNA synthesis and the production of infectious virus. Modification of the substituents on the quinolinecarboxamide scaffold resulted in analogues that proved about 7-fold more potent (average EC₅₀ = 0.03 with a SD = 0.01 µM) and that were devoid of cellular toxicity, for the concentration range tested (SI = 3333). CSFCII resistant BVDV variants were selected and were found to carry the F224P mutation in the viral RNA-dependent RNA polymerase (RdRp), whereas CSFCI resistant BVDV carried two mutations in the same region of the RdRp, i.e., N264D and F224Y. Likewise, molecular modeling revealed that F224P/Y and N264D are located in a small cavity near the fingertip domain of the pestivirus polymerase. CSFC-resistant BVDV proved to be cross-resistant to earlier reported pestivirus inhibitors (BPIP, AG110, LZ37, and BBP) that are known to target the same region of the RdRp. CSFC analogues did not inhibit the in vitro activity of recombinant BVDV RdRp but inhibited the activity of BVDV replication complexes (RCs). CSFC analogues likely interact with the fingertip of the pestivirus RdRp at the same position as BPIP, AG110, LZ37, and BBP. This indicates that this region is a “hot spot” for the inhibition of pestivirus replication.

The effect of human interferon alpha on replication of different bovine viral diarrhea virus strains

Bovine viral diarrhea virus (BVDV) exists in two main biotypes: cytopathic (cp) and noncytopathic (ncp). Although some studies were done on the effect of interferon alpha (IFN-α) on BVDV, the effect of exogenous IFN against BVDV biotypes remains unclear. In the present study, we evaluated the comparative effect of exogenous human IFN-α (HuIFN-α) on different BVDV biotypes and genotypes. The results showed that exogenous HuIFN-α greatly inhibited the growth of different BVDV biotypes and genotypes. However, HuINF-α has a significant inhibitory effect on cp biotype compared to ncp one without significant variation between different genotypes. The effect of HuIFN-α on BVDV reached the maximum level at early stages of infection (0-20 h post infection) and increased in a dose-dependent manner (10-500 U/ml). Quantitative real-time RT-PCR was used to evaluate the effect of exogenous HuIFN-α on RNA synthesis of both BVDV biotypes. HuIFN-α reduced RNA production of cp by 4 logs compared to only 2 logs for ncp strains. Additionally, the antiviral effect of IFN-α against both BVDV biotypes seems to be independent of the RNA-dependent protein kinase (PKR) activation as assayed by direct analysis of in vivo phosphorylation of eIF2-α and by 2-aminopurine (2-AP) treatment. Collectively, these results indicated that the exogenous HuIFN-α treatment has an inhibitory effect not only on cp BVDV biotype but also on the ncp BVDV. The antiviral effect of exogenous HuIFN-α was biotype, time, dose but not genotype dependent. PKR has no role in the inhibitory effect suggesting that other IFN-antiviral pathways were involved. Keywords: BVDV biotypes; HuIFN-α; RNA synthesis; PKR-independent.

The evaluation of an immunoperoxidase assay applicable in antiviral drug screening

Bovine viral diarrhea virus (BVDV) fall into cytopathic (CP) and noncytopathic (NCP) biotypes, based on their ability to kill cultured cells. NCP-BVDV can not be titrated by conventional means as used for CP-BVDV, which has impeded the identification of antiviral drugs targeting NCP-BVDV virus strains. In this study, the application of an immunoperoxidase assay in the screening of antiviral drugs was tested using two known BVDV inhibitors, ribavirin and ammonium chloride (NH4Cl). Phospholipase C inhibitor U73122 was identified to affect BVDV infection by using this immunoperoxidase assay. In addition, the results of immunoperoxidase assay were validated by real-time PCR. Taken together, the immunoperoxidase assay is a useful and versatile method suitable for antiviral drug screening targeting NCP-BVDV.

Action of Celgosivir (6 O-Butanoyl Castanospermine) against the Pestivirus BVDV: Implications for the Treatment of Hepatitis C

α-Glucosidase I inhibitors have been shown to inhibit the replication of a broad range of enveloped viruses by preventing the correct folding of their envelope glycoproteins. This study assesses the potential of 6 O-butanoyl castanospermine (cel-gosivir) as a treatment for hepatitis C virus (HCV). In the absence of an adequate culture system for HCV, the closely related virus, bovine viral diarrhoea virus (BVDV), was used as a surrogate model. Using both a plaque assay and a cytopathic effect assay, celgosivir (IC50 16 and 47 μM respectively) was shown to be more potent than N-nonyl DNJ (105 and 74 μM), castanospermine (110 and 367 μM) and N-butyl DNJ (>250 and 550 μM). Of the α-glucosi-dase inhibitors tested, only N-nonyl DNJ showed evidence of toxicity (CC50 ≥120 μM). Two-way combinations of interferon-α, ribavirin and either celgosivir or castanospermine demonstrated that each could enhance the antiviral efficacy of the others, either additively or synergistically. The observation that the number of viral genomes released from BVDV-infected cells was inhibited by either castanospermine or celgosivir in parallel with the number of infectious units was taken as confirmation that these α-glucosidase I inhibitors block the production or release of flavivirus particles.

Effect of treatment with a cationic antiviral compound on acute infection with bovine viral diarrhea virus

Bovine viral diarrhea virus (BVDV) is a widespread bovine pathogen capable of causing disease affecting multiple body systems. Previous studies have shown 2-(2-benzimidazolyl)-5-[4-(2-imidazolino)phenyl]furan dihydrochloride (DB772) effectively prevents BVDV infection in cell culture. The aim of this project was to assess the efficacy of DB772 for the prevention of acute BVDV infection. Four calves seronegative to BVDV were treated with DB772 and another 4 calves were treated with diluent only on the same dosing schedule. Each calf was subsequently challenged intranasally with BVDV. Virus was isolated consistently from untreated calves on days 4 to 8, while treated calves remained negative by virus isolation during this period. Azotemia was exhibited by all treated calves on day 4 resulting in the euthanasia of 1 calf on day 10 and the death of another on day 13. Virus was isolated from the 2 remaining treated calves on day 14 or 21. On day 21, both remaining treated calves and all 4 untreated calves had anti-BVDV antibody titers > 1:2048. This pilot study indicates that DB772 temporarily prevented acute disease due to BVDV, but carries a significant concern of renal toxicity.

Effects of interferon-tau on cattle persistently infected with bovine viral diarrhea virus

In this study, the antiviral effects of bovine interferon-tau (boIFN-tau) on bovine viral diarrhea virus (BVDV) were examined in vitro and in vivo. In the in vitro experiments, the replication of cytopathic and non-cytopathic BVDV was inhibited in the bovine cells treated with boIFN-tau. The replication of BVDV was completely suppressed by boIFN-tau at a concentration higher than 10(2) U/ml. In order to examine the effect of boIFN-tau on virus propagation in cattle persistently infected (PI) with non-cytopathic BVDV, boIFN-tau was subcutaneously administered to PI cattle at 10(5) U/kg or 10(6) U/kg body weight 5 times per week for 2 weeks. No physical abnormality such as depression was observed in the cattle during the experiment. The mean BVDV titers in the serum of the PI cattle decreased slightly during the boIFN-tau administration period with the dose of 10(6) U/kg. However, the BVDV titers in the serum returned to the pre-administration level after the final boIFN-tau administration. These results suggest that boIFN-tau demonstrates an anti-BVDV effect, reducing the BVDV level in serum transiently when injected into PI cattle.

Effect of dexamethasone administration on bulls with a localized testicular infection with bovine viral diarrhea virus

The objective of this research was to evaluate reactivation of bovine viral diarrhea virus (BVDV) following dexamethasone treatment in 4 bulls that had previously been inoculated with BVDV, 3 of which had been demonstrated to have a localized testicular infection. Bulls were housed in an isolated pasture with in-contact steers. Beginning on day 0 of this study, all bulls received a daily dose of 0.1 mg/kg body weight (BW) of dexamethasone intravenously for 5 consecutive days. Blood was collected from the in-contact steers and semen, blood, and cerebrospinal fluid were collected from the bulls during and following dexamethasone treatment. Samples were assayed for BVDV using virus isolation and reverse transcription-nested polymerase chain reaction (RT-nPCR). Serum was assayed for antibody using standard virus isolation. Virus was not isolated from blood, cerebrospinal fluid, or semen from any of the 4 bulls during the study period. One of the bulls was positive for BVDV in semen by RT-nPCR throughout the study period. The BVDV was not recovered from any in-contact control steers during the 28-day study period, nor did any of the in-contact control steers seroconvert to BVDV. Raw semen from 1 bull that was RT-nPCR positive was intravenously inoculated into 7 seronegative steers based upon the Cornell Semen Test. The BVDV could not be recovered from the steers and none of them seroconverted to BVDV. The results indicated that reactivation of BVDV in bulls with a localized testicular infection is unlikely; however, further research is necessary to determine the full potential for BVDV transmission from bulls with a localized testicular infection.

Inhibitory effect of medicinal herbs against RNA and DNA viruses

Fifteen Argentine medicinal plants were tested for their antiviral activity in vitro against herpes simplex viruses types 1 and 2 (HSV-1 and 2), bovine viral diarrhoea virus type 1 (BVDV-1), influenza virus type A (Inf A) and human immunodeficiency virus type 1 (HIV-1). Antiviral activity was evaluated by a reduction in cytopathic effect, plaque-forming units and p24 HIV-1 antigen. The Selective Index of the active extract (SI(extract) = CC50(extract)/EC50(extract)) of Coronopus didymus (SI(extract) = 110.7), Juglans australis (SI(extract) = 8.1) and Lippia alba (SI(extract) = 19.2) against BVDV-1, HSV-1 and influenza A virus, respectively, justify a further analysis. None of the seven plants assayed against HIV-1 displayed any antiviral activity. The results of this study justify the continuing isolation and characterization of the antiviral components present.

Evaluation of antiviral activity and toxicity of recombinant human interferon alfa-2a in calves persistently infected with type 1 bovine viral diarrhea virus

OBJECTIVE

To evaluate antiviral activity and toxicity of recombinant human interferon alfa-2a in calves persistently infected with noncytopathic type 1 bovine viral diarrhea virus (BVDV).

ANIMALS

5 Holstein heifers, 4 to 12 months of age.

PROCEDURES

Calves persistently infected with noncytopathic type 1 BVDV were treated with recombinant human interferon alfa-2a every other day for 12 weeks. Viral loads were measured during the treatment period and compared with pre- and post-treatment values. Complete physical examinations were performed weekly, and calves were observed daily for signs of systemic illness. Complete blood counts and serum biochemical analyses were performed before, during, and after the treatment period. Because calves developed anemia during the treatment period, bone marrow biopsy specimens were collected. Antirecombinant human interferon alfa-2a antibody concentrations in serum samples obtained before, during, and after the treatment period were measured by use of an ELISA.

RESULTS

Recombinant human interferon alfa-2a had no antiviral activity against noncytopathic type 1 BVDV in persistently infected calves. All calves developed microcytic anemia during the treatment period that persisted for up to 13 weeks after cessation of treatment. Anti-interferon antibodies were detected during the treatment period and persisted for at least 2 weeks after cessation of treatment.

CONCLUSIONS AND CLINICAL RELEVANCE

Because of lack of in vivo antiviral activity against BVDV, recombinant human interferon alfa-2a has little promise as a therapeutic agent for the treatment of BVDV infection, at least in persistently infected cattle. Furthermore, treatment was associated with adverse immunologic and hematologic effects.

Effects of interferon, ribavirin, and iminosugar derivatives on cells persistently infected with noncytopathic bovine viral diarrhea virus

Persistent infection with hepatitis C virus (HCV) is a major cause of chronic hepatitis in humans. In chronic carriers, the viral infection induces liver damage that predisposes the patient for cirrhosis and can lead to hepatocellular carcinoma. Current chemotherapies are limited to alpha interferon (IFN-alpha) used either alone or in combination with ribavirin (RBV). In addition to its limited efficacy, this treatment is frequently poorly tolerated because of its side effects. The urgently needed development of new drugs is made difficult by the lack of an in vitro or in vivo infectivity model, and no cell line has been found so far to reliably and reproducibly support HCV infection. For this reason, the closely related pestivirus bovine viral diarrhea virus (BVDV) has sometimes been used as a surrogate in vitro infectivity model. In this study we used an MDBK cell line persistently infected with noncytopathic BVDV to assess the antiviral effect of IFN-alpha and RBV, the two drugs currently in clinical use against HCV. The same system was then used to evaluate the potential of two classes of iminosugar derivates to clear noncytopathic BVDV infection from MDBK cells. We show that treatment with long-alkyl-chain deoxynojirimycin derivatives, which are inhibitors of the endoplasmic reticulum (ER)-resident alpha-glucosidases, can greatly reduce the amount of secreted enveloped viral RNA. Long-alkyl-chain deoxygalactonojirimycin derivatives, which do not inhibit ER alpha-glucosidases, were less potent but still more effective in this system than IFN-alpha or ribavirin.

Antiviral activity of Petiveria alliacea against the bovine viral diarrhea virus

BACKGROUND

Natural products are a relevant source of antiviral drugs. Five medicinal plants used in Argentina have been assayed to detect inhibition of viral growth.

METHODS

Antiviral activity of the infusions and methanolic extracts of Aristolochia macroura, Celtis spinosa, Plantago major, Schinus areira, Petiveria alliacea and four extracts obtained from the leaves and stems of the last plant were evaluated by the plaque assay.

RESULTS

P. alliacea, unlike A. macroura, C. spinosa, P. major and S. areira, inhibited bovine viral diarrhea virus (BVDV) replication. Neither P. alliacea nor the assays of the other plants were active against herpes simplex virus type 1, poliovirus type 1, adenovirus serotype 7 and vesicular stomatitis virus type 1. Four extracts of P. alliacea were assayed to detect anti-BVDV activity. Ethyl acetate (EC(50) of 25 microg/ml) and dichloromethane (EC(50) of 43 microg/ml) extracts were active; moreover, promising SI (IC(50)/EC(50)) values were obtained.

CONCLUSION

BVDV is highly prevalent in the cattle population, there are no antiviral compounds available; additionally, it is a viral model of the hepatitis C virus. For these reasons and in view of the results obtained, the isolation and characterization of the antiviral components present in the P. alliacea extracts is worth carrying out in the future.

Study of the mechanism of antiviral action of iminosugar derivatives against bovine viral diarrhea virus

The glucose-derived iminosugar derivatives N-butyl- and N-nonyl-deoxynojirimycin (DNJ) have an antiviral effect against a broad spectrum of viruses including Bovine viral diarrhea virus (BVDV). For BVDV, this effect has been attributed to the reduction of viral secretion due to an impairment of viral morphogenesis caused by the ability of DNJ-based iminosugar derivatives to inhibit ER alpha-glucosidases (N. Zitzmann, A. S. Mehta, S. Carrouée, T. D. Butters, F. M. Platt, J. McCauley, B. S. Blumberg, R. A. Dwek, and T. M. Block, Proc. Natl. Acad. Sci. USA 96:11878-11882, 1999). Here we present the antiviral features of newly designed DNJ derivatives and report for the first time the antiviral activity of long-alkyl-chain derivatives of deoxygalactonojirimycin (DGJ), a class of iminosugars derived from galactose which does not inhibit endoplasmic reticulum (ER) alpha-glucosidases. We demonstrate the lack of correlation between the ability of long-alkyl-chain DNJ derivatives to inhibit ER alpha-glucosidases and their antiviral effect, ruling out ER alpha-glucosidase inhibition as the sole mechanism responsible. Using short- and long-alkyl-chain DNJ and DGJ derivatives, we investigated the mechanisms of action of these drugs. First, we excluded their potential action at the level of the replication, protein synthesis, and protein processing. Second, we demonstrated that DNJ derivatives cause both a reduction in viral secretion and a reduction in the infectivity of newly released viral particles. Long-alkyl-chain DGJ derivatives exert their antiviral effect solely via the production of viral particles with reduced infectivity. We demonstrate that long-alkyl-chain DNJ and DGJ derivatives induce an increase in the quantity of E2-E2 dimers accumulated within the ER. The subsequent enrichment of these homodimers in secreted virus particles correlates with their reduced infectivity.

Effect of a single therapeutic dose of levamisole on bovine viral diarrhea virus infection in calves

The effect of a single therapeutic dose of levamisole in calves experimentally infected with bovine viral diarrhea virus (BVDV) was evaluated in 2 separate double-blind experiments. The infection was mild and there was no difference in severity of infection or speed of recovery between levamisole-treated and 0.9% Nacl solution-treated (control) calves. There were no significant differences between drug-treated and control calves in respect to total white blood cell, lymphocyte, and neutrophil counts, and the viral recovery data from these calves were comparable. The differences in blastogenic response of lymphocytes to the mitogen phytohemagglutinin and serum antibody titers of the 2 groups of calves were also insignificant. An increased lymphocytic hyperplasia was observed in a larger number of lymphoid tissues of drug-treated calves than in those of control calves. It appeared that a single therapeutic dose of levamisole was ineffective in altering the response of calves infected with BVDV.

Effect of levamisole on induced bovine viral diarrhea

The effect of levamisole in calves experimentally infected with bovine viral diarrhea virus was evaluated in a double-blind study. The infection was mild and there was no difference in severity of infection or speed of recovery between levamisole-treated and 0.9% NaCl solution-treated (control) calves. Also, the serum antibody titers and viral recovery data of these calves were comparable. The white blood cell counts were consistently higher in the treated group than in the control group, with the difference peaking on postinoculation day 15. The detection of marked lymphopenia in control calves but not in levamisole-treated calves indicated a potential use of levamisole in bovine viral diarrhea.