Drug delivery system based on metal-organic framework improved 5-Fluorouracil against spring viremia of carp virus

Spring viremia of carp virus (SVCV), as a high pathogenicity pathogen, has seriously restricts the healthy and sustainable development of cyprinid farming industry. In this study, we selected 5-Fluorouracil (5-Fu) as the drug model based on zeolitic imidazolate framework-8 (ZIF-8) to construct a drug delivery system (5-Fu@ZIF-8), and the anti-SVCV activity was detected in vitro and in vivo. The results showed 5-Fu@ZIF-8 was uniform cubic particle with truncated angle and smooth surface, and the particle size was 90 nm. The anti-SVCV activity in vitro results showed that the highest inhibition rate of 5-Fu was 77.93% at 40 mg/L and the inhibitory concentration at half-maximal activity (IC50) was 20.86 mg/L. For 5-Fu@ZIF-8, the highest inhibition rate was 91.36% at 16 mg/L, and the IC50 value was 5.85 mg/L. In addition, the cell viability was increased by 18.1% after 5-Fu treatment. Similarly, after 5-Fu@ZIF-8 treatment, the cell viability increased by 27.3%. Correspondingly, in vivo experimental results showed the viral loads reduced by 18.1% on the days 7 and the survival rate increased to 19.4% at 80 mg/L after 5-Fu treatment. For 5-Fu@ZIF-8, the viral loads reduced by 41.2% and the survival rate increased to 54.8%. Mechanistically, 5-Fu inhibits viral replication by regulating p53 expression and promoting early apoptosis in infected cells. All results indicated that 5-Fu@ZIF-8 improved the anti-SVCV activity; it may be a potential strategy to construct a drug-loaded system with ZIF-8 as a carrier for the prevention and treatment of aquatic diseases.

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.

Antiviral Activity of a Turbot (Scophthalmus maximus) NK-Lysin Peptide by Inhibition of Low-pH Virus-Induced Membrane Fusion

Global health is under attack by increasingly-frequent pandemics of viral origin. Antimicrobial peptides are a valuable tool to combat pathogenic microorganisms. Previous studies from our group have shown that the membrane-lytic region of turbot (Scophthalmus maximus) NK-lysine short peptide (Nkl_71–100) exerts an anti-protozoal activity, probably due to membrane rupture. In addition, NK-lysine protein is highly expressed in zebrafish in response to viral infections. In this work several biophysical methods, such as vesicle aggregation, leakage and fluorescence anisotropy, are employed to investigate the interaction of Nkl_71–100 with different glycerophospholipid vesicles. At acidic pH, Nkl_71–100 preferably interacts with phosphatidylserine (PS), disrupts PS membranes, and allows the content leakage from vesicles. Furthermore, Nkl_71–100 exerts strong antiviral activity against spring viremia of carp virus (SVCV) by inhibiting not only the binding of viral particles to host cells, but also the fusion of virus and cell membranes, which requires a low pH context. Such antiviral activity seems to be related to the important role that PS plays in these steps of the replication cycle of SVCV, a feature that is shared by other families of virus-comprising members with health and veterinary relevance. Consequently, Nkl_71–100 is shown as a promising broad-spectrum antiviral candidate.

Antiviral effect of 7-(4-benzimidazole-butoxy)-coumarin on rhabdoviral clearance via Nrf2 activation regulated by PKCα/β phosphorylation

Coumarin forms an elite class of naturally occurring compounds that possess promising antiviral therapeutic perspectives. In the previous study, we designed and synthesized a coumarin derivative, 7-(4-benzimidazole-butoxy)-coumarin (BBC), to evaluate its antiviral activity on spring viraemia of carp virus (SVCV). In this study, our results show that BBC does not affect viral adhesion and delivery from endosomes to the cytosol, indicating BBC has no inhibitory activity in the early stage of viral infection. Further data are determined that BBC significantly declines SVCV-infected apoptosis and recovers caspase-3/8/9 activity. To reveal the pathway that affects Nrf2 translocation by BBC, we examine changes in protein kinase C (PKC) in EPC cells treated with BBC. We observe that BBC results in a higher phosphorylation of PKCα/β that is involved in the activation of erythroid 2-related factor 2 (Nrf2) phosphorylation to favor Nrf2 translocation to nucleus at 24 and 48 h. In addition, the results show that BBC also up-regulates both antiviral responses, heme oxygenase-1 (HO-1) expression and cellular IFN response. Overall, this mechanism of action provides a new therapeutic target for the treatment of SVCV infection, and these results suggest that treatment with BBC is effective in reducing SVCV infection and differently regulates SVCV-induced undesirable conditions.

Synthesis and in vitro activities evaluation of arctigenin derivatives against spring viraemia of carp virus

Spring viraemia of carp virus (SVCV) is a viral fish pathogen causing high mortality in several carp species and other cultivated fish. However, robust anti-SVCV drugs currently are extremely scarce. For the purpose of seeking out anti-SVCV drugs, here a total of 35 arctigenin derivatives were designed, synthesized and evaluated for their anti-viral activities. By comparing the inhibitory concentration at half-maximal activity (IC₅₀) of the 15 screened candidate drugs (max inhibitory response surpassing 90%) in epithelioma papulosum cyprini (EPC) cells infected with SVCV, 2Q and 6 A were chosen for additional validation studies, with an IC₅₀ of 0.077 μg/mL and 0.095 μg/mL, respectively. Further experiments revealed that 2Q and 6 A could significantly decrease SVCV-induced apoptosis and have a protective effect on cell morphology at 48 and 72 h post-infection. Moreover, the reactive oxygen species (ROS) induced upon SVCV infection could be obviously inhibited by 2Q and 6 A, while SVCV-infected cells were clearly observed. On account of these findings, 2Q and 6 A could have a promising application for the treatment of infection of SVCV and provide a considerable reference for novel antivirals in aquaculture.

Synthesis and antiviral activity of a new coumarin derivative against spring viraemia of carp virus

Coumarin as a lead structure have received a considerable attention in the last three decades for the discovery of antiviral agents. Our previous study indicated that imidazole coumarins possessed antiviral activities against SVCV. Based on the structure-activity relationship in that study, a new imidazole coumarin derivative, 7-(4-benzimidazole-butoxy)-coumarin (BBC), was designed, synthesized and its anti-SVCV activity was evaluated. By comparing inhibitory concentration at half-maximal activity (IC₅₀), we found that BBC (IC₅₀ = 0.56 mg/L) possessed a higher antiviral activity than those imidazole coumarins in our previous study. Besides, BBC can significantly inhibit cell death and reduce cellular morphological damage induced by SVCV. Our further data indicated that intraperitoneal injection of BBC increased the survival rate of zebrafish by 17.5%, decreased viral titer in fish body and inhibited SVCV glycoprotein expression in kidney and spleen. In uninfected zebrafish, the expression levels of ifnγ, ifnφ1, ifnφ2 and rig1 genes were up-regulated after BBC treatment, which indicated that BBC could activate interferon response. In addition, data of the antioxidant enzymes activities and results of the antioxidant enzymes-related genes expressions suggested BBC could reduce SVCV-induced oxidative damage in infected zebrafish. Altogether, BBC is expected to be a therapeutic agent against SVCV infection in the field of aquaculture.

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

Coumarin forms an elite class of naturally occurring compounds that possess promising antiviral therapeutic perspectives. In this study, a coumarin derivative 7-[6-(2-methylimidazole) hexyloxy] coumarin (D5) was designed and synthesized to evaluate antiviral activity on a rhabdovirus, spring viraemia of carp virus (SVCV). Our results demonstrated that D5 had a robust antiviral activity with >90% inhibitory rate of SVCV expression in the host cells. And D5 significantly reduced viral-induced apoptosis and recovered virus-activated caspase-3/8/9 activities. Further data determined that SVCV could alter the cytoskeletal structure of EPC cells, characterized by a circumferential ring of microtubules and a disrupted microfilament organization, whereas cytoskeleton structure in D5-treated cells kept the normal morphology. Mechanistically speaking, D5 could interfere with SVCV replication inside or outside of cells through two different approaches. Before the process of virus entry into EPC cells, D5 had an impact on SVCV glycoprotein structure so as to disrupt viral binding to the cell surface or translocation to the cytosol. Another strategy for D5 to against SVCV was that D5 significantly suppressed SVCV-activated autophagy, which was beneficial for the host cells to restrict SVCV viral replication, accompanied by a higher phosphorylation of Akt-mTOR. In summary, our results revealed that D5 was effective in weakening SVCV infection and regulating SVCV-induced undesirable conditions, and this compound provided new therapeutic implications for the treatment of rhabdoviruses.

Highly efficient inhibition of spring viraemia of carp virus replication in vitro mediated by bavachin, a major constituent of psoralea corlifonia Lynn

As one of nine piscine viruses recognized by the International Office of Epizootics, spring viraemia of carp virus (SVCV) is an important pathogen bringing high mortality to cyprinids. Up to now, there is no approved therapy on SVCV, making them strong public health threat in aquaculture. In this study, the anti-SVCV activities of 12 plant crude extracts were investigated by using epithelioma papulosum cyprini (EPC) cells. Among these plants, Psoralea corylifolia Linn. showed the highest inhibition on SVCV replication, with an inhibitory percentage of 67.98%. Further studies demonstrated that bavachin (BVN), one of the major constituents of Psoralea corylifolia Linn., was also highly effective to SVCV infection. The half maximal inhibitory concentrations (IC₅₀) of BVN on SVCV glycoprotein and nucleoprotein expression were 0.46 (0.29-0.73) and 0.31 (0.13-0.55) mg/L, respectively. In addition, SVCV-induced apoptosis which may be negative to SVCV replication was inhibited by BVN. The apoptotic cells were decreased 21.42% for BVN compared with SVCV group. These results indicated that the inhibition of BVN on SVCV replication was, in some extent, via blocking SVCV induced apoptosis. Furthermore, cellular morphological damage induced by SVCV was also blocked by BVN treatment. Mechanistically, BVN did not affect SVCV infectivity and cannot be used for prevention of SVCV infection. Time-of-addition and viral binding assays revealed that BVN mainly inhibited the early events of SVCV replication but did not interfere with SVCV adsorption. In conclusion, BVN was considered to develop as a promising agent to treat SVCV infection.

Cell-Specific Inhibition of Paramyxovirus Maturation by Proteasome Inhibitors

Effects of proteasome inhibitors on the replication of a paramyxovirus in comparison with the effects on replication of an orthomyxovirus and rhabdovirus were investigated. Treatment of Sendai virus (SeV)-infected LLC-MK2 cells with 50 microM MG132 reduced virus growth to ca. 1/10,000, and treatment with different concentrations of MG132 reduced virus growth in a dose-dependent manner. Released amounts of viral proteins were reduced in correspondence with decrease in infectivity. The inhibition of virus maturation was confirmed by an SeV-like particle formation system. Lactacystin also impaired SeV growth and zLL impaired the growth to a lesser extent, suggesting involvement of proteasomes in the restriction of virus growth. In the presence of MG132, localizations of the M protein and viral F and HN glycoproteins on the cell membrane appeared to be partly dissociated, although the viral glycoproteins were normally transported to the cell surface. These results suggest that an early step of SeV assembly was disturbed by proteasome inhibitors. The relationship of the results with ubiquitin is also discussed. SeV maturation was less susceptible and resistant to MG132 in CV1 cells and A549 cells, respectively, indicating cell specificity of the drug effect. Release of vesicular stomatitis virus also showed high susceptibility to MG132 and release of influenza virus A/WSN/33 was only mildly susceptible to the drug in LLC-MK2 cells. Effects of proteasome inhibitors on virus maturation are thus highly cell-specific and partly virus-specific.

pH-dependent solution structure and activity of a reduced form of the host-defense peptide myticin C (Myt C) from the mussel Mytilus galloprovincialis

Myticin C (Myt C) is a highly variable host-defense peptide (HDP) associated to the immune response in the mediterranean mussel (Mytilus galloprovincialis), which has shown to be active across species due to its strong antiviral activity against a fish rhabdovirus found in fish cells overexpressing this HDP. However, the potential antimicrobial properties of any synthetic analogue of Myt C has not yet been analysed. Thus, in this work we have synthesised the sequence of the mature peptide of Myt C variant c and analysed the structure activity relationships of its reduced (non-oxidized) form (red-MytCc). In contrast to results previously reported for oxidized isoforms of mussel myticins, red-MytCc was not active against bacteria at physiological pH and showed a moderate antiviral activity against the viral haemorrhagic septicaemia (VHS) rhabdovirus. However, its chemotactic properties remained active. Structure/function studies in neutral and acid environments by means of infrared spectroscopy indicated that the structure of red-MytCc is pH dependent, with acid media increasing its alpha-helical content. Furthermore, red-MytCc was able to efficiently aggregate artificial phospholipid membranes at low pH, as well as to inhibit the Escherichia coli growth, suggesting that this activity is attributable to its more structured form in an acidic environment. All together, these results highlight the dynamic and environmentally sensitive behavior of red-Myt C in solution, and provide important insights into Myt C structure/activity relationships and the requirements to exert its antimicrobial/immunomodulatory activities. On the other hand, the pH-dependent direct antimicrobial activity of Myt C suggests that this HDP may be a suitable template for the development of antimicrobial agents that would function selectively in specific pH environments, which are sorely needed in this "antibiotic-resistance era".

In vitro inhibition of fish rhabdoviruses by Japanese flounder, Paralichthys olivaceus Mx

A homologous fish cell line stably expressing the recombinant Japanese flounder Mx (JFMx) was infected with hirame rhabdovirus (HIRRV) and viral hemorrhagic septicemia virus (VHSV), both of which are negative single-stranded RNA viruses belonging to the Rhabdoviridae family. Analysis of primary transcription of the two rhabdoviruses showed that there was lower expression level and copy number of the viral nucleoprotein transcript in the JFMx-transfected cell line than the infected, control cells, although no significant difference was observed. This suggests that JFMx may not be a potent inhibitor of rhabdoviral primary transcription. Kinetics of rhabdovirus expression by RT-PCR and quantitative real-time RT-PCR showed reduced levels of the rhabdoviral glycoprotein and nucleoprotein transcripts over time, indicating the possible role of JFMx in blocking rhabdoviral replication by interfering with the transcription of the viral subgenomic mRNAs. Significant inhibition in rhabdovirus replication consequently resulted in the synthesis of fewer viral particles. This may explain why JFMx-expressing cells are less susceptible to virus-induced cell lysis, and thus, why they would have a significantly higher survival than the infected, control cells. These results provide direct evidence that JFMx has an antiviral effect in vitro.

Influence of methisoprinol on the replication of rhabdoviruses isolated from carp (Cyprinus carpio) and catfish (Ictalurus melas): in vitro study

Rhabdoviruses constitute one of the most pathogenic viruses isolated from rainbow trout and carp culture. Several viruses were also isolated from other species of fish. These viruses are mostly associated with epizootics and heavy losses. Spring viraemia of carp virus (SVCV) and pike fry rhabdovirus (PFRV) have been the most extensively studied, due to their significant economic impact. Significant progress has been made towards controlling the major bacterial fish diseases using vaccines, but this approach has not yet been successful in preventing viral diseases in fish culture. However, for an effective therapeutic approach, specific drugs should be developed to selectively inhibit virus replication and/or stimulate antiviral protection. In this investigation we examined the in vitro influence of methisoprinol on the SVCV and virus isolated from catfish (Ictalurus melas) replication by measuring their RNA synthesis. The viruses were propagated in EPC cells and cell cultures containing methisoprinol were followed by infection with SVCV or catfish rhabdovirus suspension containing 10(7) TCID50/ml. Methisoprinol (Polfa, Poland) at concentrations of 0, 100, 200, 300, 400 and 500 microg/ml of medium (Glasgow MEM) was used in this study. The results of this study show the strong inhibition of incorporation (cpm) of [3H]-uridine into SVCV and catfish rhabdovirus RNA in cell culture exposed to methisoprinol at various concentrations. The highest percent of inhibition of viral RNA at 72 h after infection with two rhabdoviruses were observed in doses of 400 and 500 microg/ml of methisoprinol in medium. The results of this in vitro study showed that methisoprinol inhibits the rhabdoviruses isolated from carp and catfish.

A new bacilliform fathead minnow rhabdovirus that produces syncytia in tissue culture

A pathogenic bacilliform virus 130-180 nm in length and 31-47 nm in diameter was isolated from moribund fathead minnows (Pimephales promelas) exhibiting hemorrhages in their eyes and skin. A cytopathic effect of multifocal syncytia was observed in the epithelioma papulosum cyprini cell line after a 48 h incubation at 20 degrees C. A similar cytopathic effect was also observed in other cell lines tested, but not in bluegill fry, koi fin, or Chinook salmon embryo cells. The filterable agent was inactivated by exposure to 50 degrees C for 10 min, 20% ether, 2 and 50% chloroform, pH 3, and pH 10, was unaffected by 5'-iodo-2 deoxyuridine, and appeared bacilliform and occasionally bullet-shaped by electron microscopy. These results are consistent with those of rhabdoviruses. Immunodot blots performed with antisera against selected fish rhabdoviruses, an aquareovirus, and a birnavirus were all negative. River's postulates were fulfilled in fathead minnows, but the agent did not replicate or cause disease in other cyprinids or salmonids during challenge experiments. Hepatic, splenic, and renal lesions were observed during histological analysis of diseased fish from viral challenges and from the original case. Structural proteins resolved via SDS-PAGE had molecular weights similar to those reported in lyssaviruses of the family Rhabdoviridae; however, syncytia formation is not a typical cytopathic effect of rhabdoviruses. This virus, has tentatively been named the fathead minnow rhabdovirus (FHMRV) and is most similar to the members of the family Rhabdoviridae, but atypical properties like syncytia formation may justify the assignment to a novel taxon.

[Virucidal activity of disinfectants. Influence of the serum protein upon the virucidal activity of disinfectants]

Five disinfectants were tested for virucidal activity on three DNA viruses and three RNA viruses in the presence or absence of serum protein. Disinfectants of the aldehyde and halogen groups had a virucidal activity on human herpes virus, bovine rhabdo virus, human immunodeficiency virus, human adeno virus, porcine parvo virus, and polio virus. Disinfectants of the invert and amphoteric soap groups, and biganide group had a destructive effect on RNA and DNA viruses possessing an envelope. The presence of serum protein exerted great influence upon the virucidal activity of disinfectants of the invert and amphoteric soap groups.

In vitro inhibition of the replication of haemorrhagic septicaemia virus (VHSV) and African swine fever virus (ASFV) by extracts from marine microalgae

We have screened for in vitro inhibition of viral replication with extracts from the following marine microalgae: Porphyridium cruentum, Phaeodactylum tricornutum, Tetraselmis suecica, Chlorella autotrophica, Dunaliella tertiolecta, Dunaliella bardawil, Isochrysis galbana, Isochrysis galbana var Tiso, Ellipsoidon sp. and Tetraselmis tetrathele. We have used as viral models two enveloped viruses of significant economic importance, the viral hemorrhagic septicemia virus (VHSV) of salmonid fish and the African swine fever virus (ASFV). The aqueous extracts from P. cruentum, C. autotrophica and Ellipsoidon sp., produced a significant inhibition of the in vitro replication of both viruses in a dose-dependent manner. That this inhibition could be due to sulfated polysaccharides was suggested because the same pattern of viral inhibition was obtained by using exocellular extracts from microalgae enriched in these compounds and/or dextran sulfate of high molecular weight. However, the inhibition of viral replication did not correlate with the percentage of sulfatation of the exocellular polysaccharides. Extracts from marine microalgae may have prophylactic utility against fish and mammalian viral diseases.

Rhabdovirus-induced apoptosis in a fish cell line is inhibited by a human endogenous acid cysteine proteinase inhibitor

To determine the mechanisms of cell death in rhabdovirus-infected cells, we studied the infection of the epithelial papilloma of carp cell line with spring viremia of carp virus. Studies using electron microscopy, confocal microscopy, and agarose gel electrophoresis revealed changes in cell morphology and DNA fragmentation indicative of apoptosis. The virus-induced apoptosis was inhibited in cells treated with a human endogenous acid cysteine proteinase inhibitor.

Synthetic nucleosides and nucleotides. XXXV. Synthesis and biological evaluations of 5-fluoropyrimidine nucleosides and nucleotides of 3-deoxy-beta-D-ribofuranose and related compounds

1-O-Acetyl-2,5-di-O-p-chlorobenzoyl-3-deoxy-D-ribofuranose (1), derived from the antibiotic cordycepin was coupled with trimethylsilylated derivatives (2a-c) of N4-propionylcytosine, N4-p-toluoyl-5-fluorocytosine and 5-fluorouracil in the presence of trimethylsilyl trifluoromethanesulfonate (TMS-triflate) to give fully acylated nucleosides (3a-b and 3d, respectively). Selective removal of the N4-propionyl group of 3a by treatment with hydrazine hydrate gave 2',5'-di-O-p-chlorobenzoyl-3'-deoxycytidine (4). Deamination of 4 with sodium nitrite in trifluoroacetic acid afforded 2',5'-di-O-p-chlorobenzoyluridine (3c) in good yield. Compounds 3a-d were saponified to give free 3'-deoxycytidine (5a), 5-fluoro-3'-deoxycytidine (5b), 3'-deoxyuridine (5c), and 5-fluoro-3'-deoxyuridine (5d), respectively. These 3'-deoxyribonucleosides (5a-d) were then converted to corresponding 5'-monophosphate and further phosphorylated to the 5'-triphosphates by the phosphoroimidazolidate method. The nucleosides (5a-d) were examined for growth-inhibitory effects on mouse leukemic L5178Y cells, and their IC50 values (microgram/ml) were 1.8, 33, 6.5, and 18, respectively. On the other hand, the antiviral activities of these compounds on a rhabdovirus, infectious hematopoietic necrosis virus (IHNV), were moderate (IC50 = 100-500 micrograms/ml in CHSE-214 cells). The 5'-triphosphates showed remarkable inhibitory effects on DNA polymerase beta and DNA polymerase alpha-primase purified from testes of the cherry salmon, Oncorhynchus masou, but not on common DNA polymerase alpha from same source.

A comparative study of the effect of dextran sulfate on the fusion and the in vitro replication of influenza A and B, Semliki Forest, vesicular stomatitis, rabies, Sendai, and mumps virus

The effect of dextran sulfate on the fusion of a series of enveloped viruses, bearing specifically different fusion proteins, was investigated. The fusion with model- and with biological membranes was monitored by an R18 fluorescence-dequenching fusion assay. Dextran sulfate strongly suppresses the fusion of orthomxyo- (influenza A (H1N1 and H3N2 subtypes) and influenza B), of toga- (Semliki Forest virus), and of rhabdoviruses (vesicular stomatitis and rabies virus). The fusion of the paramyxo-viruses Sendai and mumps was not significantly affected by the anionic polysaccharide. The response to dextran sulfate was virus-specific, and identical for the different members of one virusfamily, bearing the same fusion protein. It was shown that dextran sulfate attaches with high affinity to the viruses studied, but not to erythrocytes. The anionic polymer appears to attach to the fusion epitope of the viral membrane. The inhibition of virus replication in vitro shows a remarkable correlation with the observed anti-fusion effects of dextran sulfate.

Inhibitory effect of a new antibiotic, guanine 7-N-oxide, on the replication of several RNA viruses

Guanine 7-N-oxide (G-7-Ox) was examined for its antiviral activity against 9 viruses based on plaque reduction, neuraminidase activity reduction, a fluorescent antibody technique or ELISA. The following viruses were included in the tests: influenza, Sendai, simian virus 5 (SV5), respiratory syncytial, western equine encephalitis, Japanese encephalitis, vesicular stomatitis, rabies and polio. G-7-Ox showed broad anti-RNA viral activity against all viruses tested, except for poliovirus. Inhibition of persistent SV5 infection by G-7-Ox indicates that its antiviral activity is independent of cytotoxicity.

Neutralization of Egtved virus pathogenicity to cell cultures and fish by monoclonal antibodies to the viral G protein

Egtved virus, the rhabdovirus causing viral haemorrhagic septicaemia in rainbow trout, was analysed at the antigen level with a future subunit vaccine in mind. Three monoclonal antibodies to the viral G protein were characterized with respect to neutralizing activity at the cell culture level, as well as their ability to protect rainbow trout fingerlings against virus infection following passive immunization. Two antibodies showed strong protective activity in fish. Only one of these antibodies was able to neutralize viral infectivity in vitro. Reduction of disulphide bonds in the G protein abolished reactivity of this antibody in immunoblotting, whereas antigen deglycosylation did not influence the binding ability of any of the antibodies. These data suggest that the G protein contains linear as well as non-linear, carbohydrate-free epitopes, which are involved in the protection against Egtved virus. However, an indirect influence of oligosaccharide side chains on epitope formation could not be excluded, since in situ inhibition of glycosylation prevented the binding of the protecting antibodies in immunofluorescence.

Prospects for treatment of viral hemorrhagic fevers with ribavirin, a broad-spectrum antiviral drug

Ribavirin, a broad-spectrum antiviral drug, is active against hemorrhagic fever viruses (with the exception of Ebola virus) in cell culture systems. In model infections with arenaviruses in guinea pigs and monkeys, ribavirin has demonstrated both prophylactic and therapeutic efficacy. In therapeutic studies it has not prevented late-onset neurologic disease. In human cases of Lassa fever, it significantly reduces mortality when administered before day 7 of illness to persons at high risk. In rodents and monkeys infected with Rift Valley fever virus, ribavirin therapy resulted in reduced mortality; prophylactic administration to volunteers infected with sandfly fever virus, Sicilian strain, prevented development of illness. Ribavirin increased the number of survivors and the mean time to death in suckling mice infected with Crimean-Congo hemorrhagic fever virus and in suckling mice infected with Hantaan virus. In the People's Republic of China, ribavirin significantly reduced mortality in patients with hemorrhagic fever with renal syndrome. Ribavirin has not been effective in animal models of filoviral and flaviviral infections. The only important adverse effect of ribavirin in humans is manageable, reversible anemia.

The efficacy of amantadine and other antiviral compounds against two salmonid viruses in vitro

Various compounds, with known clinical efficacy against human viruses, were evaluated for their ability to inhibit the growth of infectious hematopoietic necrosis virus (IHNV, a rhabdovirus), and infectious pancreatic necrosis virus (IPNV, a birnavirus), in rainbow trout cell cultures. Amantadine inhibited the plaque forming ability of IHNV, at concentrations which did not affect cell growth or morphology, although it was not active against IPNV. Metisazone and bis-benzimidazole were also effective against IHNV; but they were slightly cytotoxic. Ribavirin, as expected, was active against IPNV, but was also equally effective against IHNV, although it was cytotoxic. Several other compounds were also tested but they were not inhibitory to either virus. The attraction of amantadine is the fact that relatively easy administration should be feasible.

Screening of bacteria with antiviral activity from fresh water salmonid hatcheries

Bacteria isolated from two salmonid hatcheries were screened for antiviral activity against infectious hematopoietic necrosis virus (IHNV) to ascertain the presence of bacteria with anti-IHNV activity in the aquatic environment. Out of 710 bacterial isolates from the water and sediment samples, 190 strains showed anti-IHNV activities of more than 50% plaque reduction. These antiviral activities were detected predominantly in Pseudomonas, Aeromonas/Vibrio, and coryneforms. In one hatchery, the bacteria with antiviral activities were more prevalent in sediment samples than in water samples. Seventy-seven percent of the isolates with higher antiviral activities (greater than 90% plaque reduction) belonged to Pseudomonas.

Effect of melittin on transcription by vesiculovirus mutant and wild-type viruses

The bee venom peptide melittin activated the virion transcriptase activity of three vesiculoviruses with preservation of virion structure. The kinetics of RNA synthesis were similar to those observed with purified transcribing nucleoprotein (TNP) preparations. Six temperature-sensitive host range (tdCE) mutants of Chandipura virus displayed 1.7- to 5.5-fold greater efficiencies of transcription at 39 degrees with melittin-permeabilized virions in comparison with TNP preparations. Comparative study of other host range mutants (tdCE3) and tsB1) of vesicular stomatitis virus (VSV) New Jersey and a thermosensitive polymerase mutant (tsG114) of VSV Indiana suggested that the enhanced transcription at 39 degrees associated with melittin-activated tdCE mutants was due to the retention of host factors in the virions.

The synergism of nucleoside antibiotics combined with guanine 7-N-oxide against a rhabdovirus, infectious hematopoietic necrosis virus (IHNV)

Guanine 7-N-oxide was shown to have synergistic activity in combination with neplanocin A against a rhabdovirus, infectious hematopoietic necrosis virus (IHNV), as reported previously. We examined further the antiviral activity of guanine 7-N-oxide in combination with other nucleoside antibiotics against IHNV. Synergism was seen between guanine 7-N-oxide and D-eritadenine or cordycepin. It is considered that compounds inhibiting RNA methylation show synergism with guanine 7-N-oxide.

Antiviral activity and its mechanism of guanine 7-N-oxide on DNA and RNA viruses derived from salmonid

Guanine 7-N-oxide produced by Streptomyces sp. was found to inhibit in vitro the replication of herpes virus (Oncorhynchus masou virus, OMV), rhabdo virus (infectious hematopoietic necrosis virus, IHNV) and a bi-segmented double-strand virus (infectious pancreatic necrosis virus, IPNV) derived from salmonids with IC50 values of about 10 micrograms/ml, 20 micrograms/ml and 32 micrograms/ml, respectively. The agent was not toxic for the host cells (chinook salmon embryo, CHSE-214) at the IC50 concentrations. Labeling of IHNV viral RNA and host cellular DNA and RNA with [3H]uridine and [3H]thymidine during drug treatment showed that guanine 7-N-oxide did not reduce the incorporation of these precusors into RNA and DNA. The anti-IHNV activity of guanine 7-N-oxide was enhanced synergistically by neplanocin A, an inhibitor of RNA methylation. The mechanism of action of guanine 7-N-oxide is discussed, in regard to maturation of viral messenger RNA including capping.

Action of human lymphoblastoid interferon on HeLa cells infected with RNA-containing animal viruses

Protein synthesis in interferon-treated HeLa cells infected by different animal RNA viruses has been studied. Synthesis of vesicular stomatitis virus (VSV) proteins was not detected in cells treated with concentrations of HuIFN-alpha (Ly) above 10 IU/ml. No specific inhibition of glycosylation of the G protein was observed. In addition, inhibition of host protein synthesis in IFN-treated cells occurred when high multiplicities of VSV were used, even though no viral protein synthesis was detected. For other viruses, such as Newcastle disease virus, Semliki Forest virus, encephalomyocarditis virus and poliovirus, treatment of cells with interferon also led to inhibition of viral protein synthesis. However, influenza virus and reovirus protein synthesis in interferon-treated cells stayed at control levels. The finding of viral translation in influenza virus and reovirus-infected cells treated with interferon suggests that, at least for these two systems, the antiviral state is not mediated by the bulk inhibition of viral protein synthesis through the dsRNA-activated protein kinase, or the 2'-5' oligo(A) system.

A plaque assay for Mount Elgon bat virus based on intrinsic interference

A plaque count infectivity assay was developed in which chick cells infected with the Mount Elgon bat virus were completely resistant to superinfection with large doses of Sendai virus. Several variables markedly affected the assay sensitivity. The defined plaque assay was simple, highly reproducible and sensitive. It allowed determination of virus neutralizing antibody in a simple and reproducible test. Both actinomycin D and 5-iododeoxyuridine were without effect on plaque formation.