Inhibition of rabies virus multiplication by siRNA delivered through adenoviral vector in vitro in BHK-21 cells and in vivo in mice

Multi-targeted gene silencing strategies inhibit replication of Canine morbillivirus

BACKGROUND

Canine morbilivirus (canine distemper virus, CDV) is a highly contagious pathogen associated with high morbidity and mortality in susceptible carnivores. Although there are CDV vaccines available, the disease poses a huge threat to dogs and wildlife hosts due to vaccine failures and lack of effective treatment. Thus, the development of therapeutics is an urgent need to achieve rapid outbreak control and reduce mortality in target species. Gene silencing by RNA interference has emerged as a promising therapeutic approach against different human and animal viruses. In this study, plasmid-based short hairpin RNAs (shRNAs) against three different regions in either CDV nucleoprotein (N), or large polymerase (L) genes and recombinant adenovirus-expressing N-specific multi-shRNAs were generated. Viral cytopathic effect, virus titration, plaque-forming unit reduction, and real-time quantitative RT-PCR analysis were used to check the efficiency of constructs against CDV.

RESULTS

In CDV-infected VerodogSLAM cells, shRNA-expressing plasmids targeting the N gene markedly inhibited the CDV replication in a dose-dependent manner, with viral genomes and titers being decreased by over 99%. Transfection of plasmid-based shRNAs against the L gene displayed weaker inhibition of viral RNA level and virus yield as compared to CDV N shRNAs. A combination of shRNAs targeting three sites in the N gene considerably reduced CDV RNA and viral titers, but their effect was not synergistic. Recombinant adenovirus-expressing multiple shRNAs against CDV N gene achieved a highly efficient knockdown of CDV N mRNAs and successful inhibition of CDV replication.

CONCLUSIONS

We found that this strategy had strong silencing effects on CDV replication in vitro. Our findings indicate that the delivery of shRNAs using plasmid or adenovirus vectors potently inhibits CDV replication and provides a basis for the development of therapeutic strategies for clinical trials.

Trying to treat the untreatable: experimental approaches to clear rabies virus infection from the CNS

Rabies virus causes an invariably fatal encephalitis following the onset of clinical disease. Despite the availability of safe and effective vaccines, the clinical stages of rabies encephalitis remain untreatable, with few survivors being documented. A principal obstacle to the treatment of rabies is the neurotropic nature of the virus, with the blood-brain barrier size exclusion limit rendering the delivery of antiviral drugs and molecules to the central nervous system inherently problematic. This review focuses on efforts to try and overcome barriers to molecule delivery to treat clinical rabies and overviews current progress in the development of experimental live rabies virus vaccines that may have future applications in the treatment of clinical rabies, including the attenuation of rabies virus vectors through either the duplication or mutation of existing genes or the incorporation of non-viral elements within the genome. Rabies post-infection treatment (PIT) remains the holy grail of rabies research.

Lentiviral-mediated delivery of classical swine fever virus Erns gene into porcine kidney-15 cells for production of recombinant ELISA diagnostic antigen

Classical swine fever virus (CSFV), a member of the Pestivirus genus within the Flaviviridae family causes contagious fatal disease in swine. Antibodies against E2, Erns and NS3 proteins of virus can be detected in infected animals. Development of an ELISA coating antigen to improve the sensitivity of detecting Erns-specific antibodies in pig sera is always desirable for diagnosis as well as for differentiation of infected from vaccinated animals. In present study, a lentivirus-based gene delivery system was used to develop a stable PK-15 cell line expressing Erns (PK-Erns) for production of diagnostic antigen. The Lenti-Erns virus was purified from the supernatant of co-transfected 293LTV cells and used to transduce PK-15 cells. The homogenous PK-Erns cell line was produced by single cell cloning by monitoring eGFP expression. The Erns gene in the genomic DNA and RNA transcripts in total RNA isolated from PK-Erns cells were detected by PCR and RT-PCR, respectively. Expression of 45 kDa Erns glycoprotein was detected in western blot using CSFV-specific hyperimmune sera. The use of PK-Erns cell lysate as antigen in serial dilution and single dilution ELISAs with known positive and negative pig sera was investigated. The PK-Erns ELISA revealed sensitivity equivalent to commercial HerdChek ELISA kit. The sensitivity, specificity and accuracy of the PK-Erns ELISA was 95%, 100% and 96.66%, respectively compared to ELISA using purified CSFV as coating antigen. When field pig sera (n = 69) were tested in PK-Erns ELISA, a significant correlation between the titers from serial dilution and single dilution ELISA was observed. This indicated that PK-Erns cell line can serve as continuous source of ELISA diagnostic antigen for detection of CSFV-specific antibodies in pig sera.

A review on current status of antiviral siRNA

Viral diseases like influenza, AIDS, hepatitis, and Ebola cause severe epidemics worldwide. Along with their resistant strains, new pathogenic viruses continue to be discovered so creating an ongoing need for new antiviral treatments. RNA interference is a cellular gene‐silencing phenomenon in which sequence‐specific degradation of target mRNA is achieved by means of complementary short interfering RNA (siRNA) molecules. Short interfering RNA technology affords a potential tractable strategy to combat viral pathogenesis because siRNAs are specific, easy to design, and can be directed against multiple strains of a virus by targeting their conserved gene regions. In this review, we briefly summarize the current status of siRNA therapy for representative examples from different virus families. In addition, other aspects like their design, delivery, medical significance, bioinformatics resources, and limitations are also discussed.

Computational design of potential siRNA molecules for silencing nucleoprotein gene of rabies virus

Aim: Rabies virus infections are a global threat to human and animal health, yet no progressive curative therapy has been developed. In this study, the nucleoprotein gene of rabies virus which is responsible for viral infection was used as a target to design our desired siRNA. Methods: The conserved regions were analyzed by doing alignment of sequences from different strains. Subsequently, different computational tools were used for designing and validation of siRNA molecules. Results: We identified four probable siRNA molecules from twelve different strains of rabies virus which may silence the nucleoprotein gene and inhibit the multiplication of the virus. Conclusion: Our study may help to take an effective therapeutic approach against rabies virus and lead to better control of rabies in humans.

Rabies - epidemiology, pathogenesis, public health concerns and advances in diagnosis and control: a comprehensive review

Rabies is a zoonotic, fatal and progressive neurological infection caused by rabies virus of the genus Lyssavirus and family Rhabdoviridae. It affects all warm-blooded animals and the disease is prevalent throughout the world and endemic in many countries except in Islands like Australia and Antarctica. Over 60,000 peoples die every year due to rabies, while approximately 15 million people receive rabies post-exposure prophylaxis (PEP) annually. Bite of rabid animals and saliva of infected host are mainly responsible for transmission and wildlife like raccoons, skunks, bats and foxes are main reservoirs for rabies. The incubation period is highly variable from 2 weeks to 6 years (avg. 2-3 months). Though severe neurologic signs and fatal outcome, neuropathological lesions are relatively mild. Rabies virus exploits various mechanisms to evade the host immune responses. Being a major zoonosis, precise and rapid diagnosis is important for early treatment and effective prevention and control measures. Traditional rapid Seller's staining and histopathological methods are still in use for diagnosis of rabies. Direct immunofluoroscent test (dFAT) is gold standard test and most commonly recommended for diagnosis of rabies in fresh brain tissues of dogs by both OIE and WHO. Mouse inoculation test (MIT) and polymerase chain reaction (PCR) are superior and used for routine diagnosis. Vaccination with live attenuated or inactivated viruses, DNA and recombinant vaccines can be done in endemic areas. This review describes in detail about epidemiology, transmission, pathogenesis, advances in diagnosis, vaccination and therapeutic approaches along with appropriate prevention and control strategies.

Use of rapid fluorescent focus inhibition test (RFFIT) for in vitro evaluation of anti-rabies activity

Even in the twenty-first century, rabies remains one of the most dreaded diseases in many parts of the world. An effective chemotherapeutic still remains elusive. The present study was aimed at in vitro evaluation of crude extracts of Allamanda cathartica and Cynodon dactylon for their potential anti-rabies activity based on the principle of immunofluorescence. The extracts were tested for cytotoxicity and screened for the presence of phytochemicals. While A. cathartica extracts were found to be non-toxic, the CC₅₀ of C. dactylon (water and methanol) cold extracts were found to be 8.17 and 9.20 mg/mL respectively on BHK-21 cell line. Rapid Fluorescent Focus Inhibition Test (RFFIT) was used to evaluate anti-rabies activities of these plants against the rabies challenge virus standard strain. We observed 50% inhibition of 10 TCID₅₀ CVS at 5 mg/mL (IC₅₀) whereas florescence (no inhibition) was observed with A. cathartica extracts. The present study highlights the use of modified RFFIT as a method of choice for testing anti-rabies activity over assays based on evaluation of cytopathic effect.

Rabies Control and Treatment: From Prophylaxis to Strategies with Curative Potential

Rabies is an acute, fatal, neurological disease that affects almost all kinds of mammals. Vaccination (using an inactivated rabies vaccine), combined with administration of rabies immune globulin, is the only approved, effective method for post-exposure prophylaxis against rabies in humans. In the search for novel rabies control and treatment strategies, live-attenuated viruses have recently emerged as a practical and promising approach for immunizing and controlling rabies. Unlike the conventional, inactivated rabies vaccine, live-attenuated viruses are genetically modified viruses that are able to replicate in an inoculated recipient without causing adverse effects, while still eliciting robust and effective immune responses against rabies virus infection. A number of viruses with an intrinsic capacity that could be used as putative candidates for live-attenuated rabies vaccine have been intensively evaluated for therapeutic purposes. Additional novel strategies, such as a monoclonal antibody-based approach, nucleic acid-based vaccines, or small interfering RNAs (siRNAs) interfering with virus replication, could further add to the arena of strategies to combat rabies. In this review, we highlight current advances in rabies therapy and discuss the role that they might have in the future of rabies treatment. Given the pronounced and complex impact of rabies on a patient, a combination of these novel modalities has the potential to achieve maximal anti-rabies efficacy, or may even have promising curative effects in the future. However, several hurdles regarding clinical safety considerations and public awareness should be overcome before these approaches can ultimately become clinically relevant therapies.

Subversion of the Immune Response by Rabies Virus

Rabies has affected mankind for several centuries and is one of the oldest known zoonoses. It is peculiar how little is known regarding the means by which rabies virus (RABV) evades the immune response and kills its host. This review investigates the complex interplay between RABV and the immune system, including the various means by which RABV evades, or advantageously utilizes, the host immune response in order to ensure successful replication and spread to another host. Different factors that influence immune responses—including age, sex, cerebral lateralization and temperature—are discussed, with specific reference to RABV and the effects on host morbidity and mortality. We also investigate the role of apoptosis and discuss whether it is a detrimental or beneficial mechanism of the host’s response to infection. The various RABV proteins and their roles in immune evasion are examined in depth with reference to important domains and the downstream effects of these interactions. Lastly, an overview of the means by which RABV evades important immune responses is provided. The research discussed in this review will be important in determining the roles of the immune response during RABV infections as well as to highlight important therapeutic target regions and potential strategies for rabies treatment.

Small Non-coding RNAs Associated with Viral Infectious Diseases of Veterinary Importance: Potential Clinical Applications

MicroRNAs (miRNAs) represent a class of small non-coding RNA (sncRNA) molecules that can regulate mRNAs by inducing their degradation or by blocking translation. Considering that miRNAs are ubiquitous, stable, and conserved across animal species, it seems feasible to exploit them for clinical applications. Unlike in human viral diseases, where some miRNA-based molecules have progressed to clinical application, in veterinary medicine, this concept is just starting to come into view. Clinically, miRNAs could represent powerful diagnostic tools to pinpoint animal viral diseases and/or prognostic tools to follow up disease progression or remission. Additionally, the possible consequences of miRNA dysregulation make them potential therapeutic targets and open the possibilities to use them as tools to generate viral disease-resistant livestock. This review presents an update of preclinical studies on using sncRNAs to combat viral diseases that affect pet and farm animals. Moreover, we discuss the possibilities and challenges of bringing these bench-based discoveries to the veterinary clinic.

Protection of mice against lethal rabies virus challenge using short interfering RNAs (siRNAs) delivered through lentiviral vector

The antiviral potential of small interfering RNAs (siRNAs) targeting rabies virus (RV) polymerase (L) and nucleoprotein (N) genes delivered through lentiviral vector was investigated. For in vitro evaluation, siRNAs expressing BHK-21 cell lines (BHK-L and BHK-N) were developed using transduction with Lenti-L and Lenti-N lentiviruses encoding siRNAs against RV-L and N genes, respectively. When these cell lines were challenged in vitro with RV Pasteur virus-11 (PV-11) strain, there was reduction in number of RV-specific foci and target gene transcripts indicating inhibitory effect on RV multiplication. For in vivo evaluation, mice were treated intracerebrally with lentiviruses and challenged with 20 LD₅₀ of RV challenge virus standard-11 (CVS-11) strain by intramuscular route in masseter muscle. Five out of eight mice treated with Lenti-N survived indicating 62.5 % protection. The control and Lenti-L-treated mice died within 7–10 days indicating lethal nature of challenge virus and no protection. These results demonstrated that siRNA targeting RV-N could not only inhibit RV multiplication, but also conferred protection in mice against lethal RV challenge. These findings have implication on therapeutic use of siRNA targeting RV-N against RV infection.

Preventive effects of siRNA targeting PPARγ gene on steroid-induced osteonecrosis in rabbits

PURPOSES/AIM: Glucocorticoid steroids can induce expression of PPARγ gene and enhance adipogenesis by bone marrow mesenchymal stem cells (BMSCs), which may result in osteonecrosis of the femoral head. Currently, there are no medications available to prevent steroid-induced osteonecrosis. We hypothesized that siRNA targeting PPARγ gene may prevent steroid-induced adipogenesis and osteonecrosis in rabbit. The purpose of this study was to evaluate the preventive effects of siRNA targeting PPARγ gene on steroid-induced adipogenesis and osteonecrosis.

METHODS

Forty-eight healthy New Zealand rabbits were randomized into four groups with Group M treated with dexamethasone only, Group S with dexamethasone and a recombinant adenovirus shuttle vector carrying siRNA targeting PPARγ gene, Group Con with dexamethasone and a vector carrying irrelative sequence, and Group N with no treatment serving as control. Expressions of the PPARγ, osteocalcin and Runx2 genes, as well as histopathologic changes were evaluated.

RESULTS

The levels of PPARγ gene expression were decreased while the levels of osteocalcin and Runx2 gene expression were increased in rabbits treated with dexamethasone and recombinant adenovirus shuttle vector carrying siRNA targeting PPARγ gene (Group S), compared to rabbits treated either with dexamethasone alone (Group M) or with both dexamethasone and a vector carrying irrelative sequence (Group Con). The marrow necrosis, adipocyte hypertrophy and proliferation, diminished hematopoiesis, thinner and sparse trabeculae, and increased empty osteocyte lacunae in the femoral head were observed in Group M and Group Con rabbits. However, no such changes were seen in Group S rabbits that were treated with dexamethasone and a recombinant adenovirus shuttle vector carrying siRNA targeting PPARγ gene.

CONCLUSION

siRNA targeting PPARγ gene can inhibit adipogenic differentiation of BMSCs and prevent steroid-induced osteonecrosis in rabbit. The inhibition of bone-marrow adipogenesis and concomitant enhancement of osteogenesis with RNAi may provide a novel approach to the prevention of steroid-induced osteonecrosis.

Evaluation of single and dual siRNAs targeting rabies virus glycoprotein and nucleoprotein genes for inhibition of virus multiplication in vitro

Small interfering RNAs (siRNAs) targeting rabies virus (RV) glycoprotein (G) and nucleoprotein (N) genes were evaluated as antiviral agents against rabies virus in vitro in BHK-21 cells. To select effective siRNAs targeting RV-G, a plasmid-based transient co-transfection approach was used. In this, siRNAs were expressed as short hairpin RNAs (shRNAs), and their ability to inhibit RV-G gene expression was evaluated in cells transfected with a plasmid expressing RV-G. The nine different siRNAs designed to target RV-G exhibited varying degrees of knockdown of RV-G gene expression. One siRNA (si-G7) with considerable effect in knockdown of RV-G expression also demonstrated significant inhibition of RV multiplication in BHK-21 cells after in vitro challenge with the RV Pasteur virus-11 (PV-11) strain. A decrease in the number of fluorescent foci in siRNA-treated cells and a reduction (86.8 %) in the release of RV into infected cell culture supernatant indicated the anti-rabies potential of siRNA. Similarly, treatment with one siRNA targeting RV-N resulted in a decrease in the number of fluorescent foci and a reduction (85.9 %) in the release of RV. As a dual gene silencing approach where siRNAs targeting RV-G and RV-N genes were expressed from single construct, the anti-rabies-virus effect was observed as an 87.4 % reduction in the release of RV. These results demonstrate that siRNAs targeting RV-G and N, both in single and dual form, have potential as antiviral agent against rabies.

Adeno-associated viruses serotype 2-mediated RNA interference efficiently inhibits rabies virus replication in vitro and in vivo

To investigate the potential of adeno-associated viruses serotype 2 (AAV2)-mediated RNA interference (RNAi) as an antiviral agent against rabies, recombinant AAV2 vectors expressing siRNA targeting the nucleoprotein (N) gene of rabies virus (RABV) (rAAV-N796) were constructed and evaluated. When NA cells pretreated with rAAV-N796 were challenged with RABV, there was a 37.8 ± 3.4% to 55.1 ± 5.3% reduction in RABV virus titer. When cells pre-challenged with RABV were treated with rAAV-N796, there was a 4.4 ± 1.4 to 28.8 ± 3.2% reduction in RABV virus titer. Relative quantification of RABV transcripts using real-time PCR and Western blot revealed that the knockdown of RABV-N gene transcripts was based on the rAAV-N796 inoculation titer. When any NA cells were treated with rAAV-N796 before or after challenged with RABV, significant reduction in virus titer was observed in both administrations. Mice treated intracerebrally with rAAV-N796 exhibited 50 ± 5.3 and 62.5 ± 4.7% protection when challenged intracerebrally or intramuscally, respectively, with lethal RABV. When mice treated intramuscularly with rAAV-N796 were challenged intramuscularly with lethal RABV, they exhibited 37.5 ± 3.7% protection. When mice were intracerebrally and intramuscularly with rAAV-N796 24 hr after exposure to RABV infection, they exhibited 25 ± 4.1% protection The N gene mRNA levels in the brains of challenged mice with three different administrations were reduced (55, 68, 32 and 25%, respectively). These results indicated that AAV2 vector-mediated siRNA delivery in vitro in NA cells inhibited RABV multiplication, inhibited RABV multiplication in vivo in the mice brain and imparted partial protection against lethal rabies. So, it may have a potential to be used as an alternative antiviral approach against rabies.

Small interfering RNAs targeting the rabies virus nucleoprotein gene

Rabies virus (RABV) infection continues to be a global threat to human and animal health, yet no curative therapy has been developed. RNA interference (RNAi) therapy, which silences expression of specific target genes, represents a promising approach for treating viral infections in mammalian hosts. We designed six small interfering (si)RNAs (N473, N580, N783, N796, N799 and N1227) that target the conserved region of the RABV challenge virus standard (CVS)-11 strain nucleoprotein (N) gene. Using a plasmid-based transient expression model, we demonstrated that N796, N580 and N799 were capable of significantly inhibiting viral replication in vitro and in vivo. These three siRNAs effectively suppressed RABV expression in infected baby hamster kidney-21 (BHK-21) cells, as evidenced by direct immunofluorescence assay, viral titer measurements, real-time PCR, and Western blotting. In addition, liposome-mediated siRNA expression plasmid delivery to RABV-infected mice significantly increased survival, compared to a non-liposome-mediated delivery method. Collectively, our results showed that the three siRNAs, N796, N580 and N799, targeting the N gene could potently inhibit RABV CVS-11 reproduction. These siRNAs have the potential to be developed into new and effective prophylactic anti-RABV drugs.