Feline Infectious Peritonitis Coronavirus Research Articles

Abdominal ultrasonographic findings of cats with feline infectious peritonitis: an update.

The aim of this study was to describe the abdominal ultrasonographic findings in cats with confirmed or presumed feline infectious peritonitis (FIP). This was a retrospective study performed in an academic veterinary hospital. The diagnosis of FIP was reached on review of history, signalment, clinical presentation, complete blood count, biochemistry panel, peritoneal fluid analysis, cytology and/or histopathology results from abnormal organs, and/or molecular testing (immunohistochemical or FIP coronavirus [FCoV] RT-PCR). Cats with confirmed FIP by molecular testing or with a highly suspicious diagnosis of FIP were included. Abdominal ultrasound examination findings were reviewed. In total, 25 cats were included. Common clinical signs/pathology findings included hyperglobulinemia (96%), anorexia/hyporexia (80%) and lethargy (56%). Abdominal ultrasound findings included effusion in 88% and lymphadenopathy in 80%. Hepatic changes were noted in 80%, the most common being hepatomegaly (58%) and a hypoechoic liver (48%). Intestinal changes were noted in 68% of cats, characterized by asymmetric wall thickening and/or loss of wall layering, with 52% being ileocecocolic junction and/or colonic in location. Splenic changes were present in 36% of cats, including splenomegaly, mottled parenchyma and hypoechoic nodules. Renal changes were present in 32%, encompassing a hypoechoic subcapsular rim and/or cortical nodules. Mesenteric and peritoneal abnormalities were seen in 28% and 16% of cats, respectively. Most cats (92%) had two or more locations of abdominal abnormalities on ultrasound. The present study documents a wider range and distribution of ultrasonographic lesions in cats with FIP than previously reported. The presence of effusion and lymph node, hepatic and/or gastrointestinal tract changes were the most common findings, and most of the cats had a combination of two or more abdominal abnormalities.

Stabilization of the Dimeric State of SARS-CoV-2 Main Protease by GC376 and Nirmatrelvir

The main protease (Mpro or 3CLpro) is an enzyme that is evolutionarily conserved among different genera of coronaviruses. As it is essential for processing and maturing viral polyproteins, Mpro has been identified as a promising target for the development of broad-spectrum drugs against coronaviruses. Like SARS-CoV and MERS-CoV, the mature and active form of SARS-CoV-2 Mpro is a dimer composed of identical subunits, each with a single active site. Individual monomers, however, have very low or no catalytic activity. As such, inhibition of Mpro can be achieved by molecules that target the substrate binding pocket to block catalytic activity or target the dimerization process. In this study, we investigated GC376, a transition-state analog inhibitor of the main protease of feline infectious peritonitis coronavirus, and Nirmatrelvir (NMV), an oral, bioavailable SARS-CoV-2 Mpro inhibitor with pan-human coronavirus antiviral activity. Our results show that both GC376 and NMV are capable of strongly binding to SARS-CoV-2 Mpro and altering the monomer-dimer equilibrium by stabilizing the dimeric state. This behavior is proposed to be related to a structured hydrogen-bond network established at the Mpro active site, where hydrogen bonds between Ser1' and Glu166/Phe140 are formed in addition to those achieved by the latter residues with GC376 or NMV.

Both Boceprevir and GC376 efficaciously inhibit SARS-CoV-2 by targeting its main protease

COVID-19 was declared a pandemic on March 11 by WHO, due to its great threat to global public health. The coronavirus main protease (Mpro, also called 3CLpro) is essential for processing and maturation of the viral polyprotein, therefore recognized as an attractive drug target. Here we show that a clinically approved anti-HCV drug, Boceprevir, and a pre-clinical inhibitor against feline infectious peritonitis (corona) virus (FIPV), GC376, both efficaciously inhibit SARS-CoV-2 in Vero cells by targeting Mpro. Moreover, combined application of GC376 with Remdesivir, a nucleotide analogue that inhibits viral RNA dependent RNA polymerase (RdRp), results in sterilizing additive effect. Further structural analysis reveals binding of both inhibitors to the catalytically active side of SARS-CoV-2 protease Mpro as main mechanism of inhibition. Our findings may provide critical information for the optimization and design of more potent inhibitors against the emerging SARS-CoV-2 virus.

Repurposing old drugs as antiviral agents for coronaviruses

BackgroundNew therapeutic options to address the ongoing coronavirus disease 2019 (COVID-19) pandemic are urgently needed. One possible strategy is the repurposing of existing drugs approved for other indications as antiviral agents for severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). Due to the commercial unavailability of SARS-CoV-2 drugs for treating COVID-19, we screened approximately 250 existing drugs or pharmacologically active compounds for their inhibitory activities against feline infectious peritonitis coronavirus (FIPV) and human coronavirus OC43 (HCoV-OC43), a human coronavirus in the same genus (Betacoronavirus) as SARS-CoV-2. MethodsFIPV was proliferated in feline Fcwf-4 cells and HCoV-OC43 in human HCT-8 cells. Viral proliferation was assayed by visualization of cytopathic effects on the infected Fcwf-4 cells and immunofluorescent assay for detection of the nucleocapsid proteins of HCoV-OC43 in the HCT-8 cells. The concentrations (EC50) of each drug necessary to diminish viral activity to 50% of that for the untreated controls were determined. The viabilities of Fcwf-4 and HCT-8 cells were measured by crystal violet staining and MTS/PMS assay, respectively. ResultsFifteen out of the 252 drugs or pharmacologically active compounds screened were found to be active against both FIPV and HCoV-OC43, with EC50 values ranging from 11 nM to 75 μM. They are all old drugs as follows, anisomycin, antimycin A, atovaquone, chloroquine, conivaptan, emetine, gemcitabine, homoharringtonine, niclosamide, nitazoxanide, oligomycin, salinomycin, tilorone, valinomycin, and vismodegib. ConclusionAll of the old drugs identified as having activity against FIPV and HCoV-OC43 have seen clinical use in their respective indications and are associated with known dosing schedules and adverse effect or toxicity profiles in humans. Those, when later confirmed to have an anti-viral effect on SARS-CoV-2, should be considered for immediate uses in COVID-19 patients.

Artificial intelligence approach fighting COVID-19 with repurposing drugs

BackgroundThe ongoing COVID-19 pandemic has caused more than 193,825 deaths during the past few months. A quick-to-be-identified cure for the disease will be a therapeutic medicine that has prior use experiences in patients in order to resolve the current pandemic situation before it could become worsening. Artificial intelligence (AI) technology is hereby applied to identify the marketed drugs with potential for treating COVID-19. MethodsAn AI platform was established to identify potential old drugs with anti-coronavirus activities by using two different learning databases; one consisted of the compounds reported or proven active against SARS-CoV, SARS-CoV-2, human immunodeficiency virus, influenza virus, and the other one containing the known 3C-like protease inhibitors. All AI predicted drugs were then tested for activities against a feline coronavirus in in vitro cell-based assay. These assay results were feedbacks to the AI system for relearning and thus to generate a modified AI model to search for old drugs again. ResultsAfter a few runs of AI learning and prediction processes, the AI system identified 80 marketed drugs with potential. Among them, 8 drugs (bedaquiline, brequinar, celecoxib, clofazimine, conivaptan, gemcitabine, tolcapone, and vismodegib) showed in vitro activities against the proliferation of a feline infectious peritonitis (FIP) virus in Fcwf-4 cells. In addition, 5 other drugs (boceprevir, chloroquine, homoharringtonine, tilorone, and salinomycin) were also found active during the exercises of AI approaches. ConclusionHaving taken advantages of AI, we identified old drugs with activities against FIP coronavirus. Further studies are underway to demonstrate their activities against SARS-CoV-2 in vitro and in vivo at clinically achievable concentrations and doses. With prior use experiences in patients, these old drugs if proven active against SARS-CoV-2 can readily be applied for fighting COVID-19 pandemic.

Pyridine N-oxide derivatives are inhibitory to the human SARS and feline infectious peritonitis coronavirus in cell culture

Objectives: Evaluation of a wide variety of pyridine N-oxide derivatives on their inhibitory activity against feline coronavirus (FIPV strain) and human SARS-CoV (Frankfurt strain-1) in cell culture. Methods: FIPV and SARS-CoV were exposed to confluent Crandel feline kidney (CRFK) and simian kidney (Vero) cell cultures in the presence of serial concentrations of the test compounds. The anti-cytopathic activity of the pyridine N-oxide derivatives was monitored by spectrophotometric analysis. Results and conclusions: A wide variety of pyridine N-oxide derivatives have been found to be inhibitory against feline coronavirus (FIPV strain) and human SARS-CoV (Frankfurt strain-1) in CRFK and simian kidney (Vero) cell cultures, respectively. The oxide part on the pyridine moiety proved indispensable for anti-coronavirus activity. The potency and virus specificity of the pyridine N-oxide derivatives varied depending the nature and specific location of substituents (i.e. alkyl, halogeno, nitro, etc.) on the different parts of the molecule. The most selective compounds were active in the higher microgram per litre range, being non-toxic at 50–100 mg/L. There was a poor structure-antiviral activity relationship (SAR) for the pyridine N-oxide derivatives against Fe-CoV and SARS-CoV. One of the most active and selective compounds was shown to inhibit Fe-CoV replication at the transcriptional level.

Inhibitory effects of recombinant feline interferon on the replication of feline enteropathogenic viruses in vitro

Antiviral activities of a recombinant feline interferon (rFeIFN) KT-80 were evaluated against feline enteropathogenic viruses in feline and canine cell lines. Sensitivity to antiviral activities of the rFeIFN varied with cell types; Felis catus whole fetus (fcwf-4) cells were more sensitive than Crandell feline kidney cells, but no sensitivity was found for Madin-Darby canine kidney cells when vesicular stomatitis virus was used as a challenge virus. Reductions were generally IFN dose-dependent and were more consistent when the cells were continuously treated with the rFeIFN than when they were pretreated only before viral challenge. Compared with each virus control culture of fcwf-4 cells, yields of rotavirus, feline panleukopenia virus (FPLV), feline calicivirus and feline infectious peritonitis coronavirus were reduced by ranges of 1.3 to ⩽3.1 log 10, 0.6 log 2, 0.8 to 3.7 log 10 and 0.5 to 0.6 log 10, respectively, in the cultures continuously treated with 10 to 10000 U of the rFeIFN. The yield reduction of FPLV was considered to be in part attributable to inhibition of cell growth by the rFeIFN supplemented in the medium.

Coronavirus Infection in Cats

Cats are susceptible to natural infection with several strains of feline coronavirus that result in either effusive and noneffusive feline infectious peritonitis or enteritis. Excretion of coronavirus by infected cats into the environment occurs by way of feces, oronasal secretions, and possibly urine. Clinical diagnosis of coronavirus infection is made by evaluating the case history, physical findings, laboratory results, and coronavirus antibody titers as well as ruling out analogous diseases. An intranasal temperature-sensitive feline infectious peritonitis coronavirus vaccine is available for use in healthy cats 16 weeks of age or older.

A novel glycoprotein of feline infectious peritonitis coronavirus contains a KDEL-like endoplasmic reticulum retention signal.

A new protein of feline infectious peritonitis coronavirus (FIPV) was discovered in lysates of [35S]cysteine-labeled infected cells. Expression of open reading frame (ORF) 6b of FIPV in recombinant vaccinia virus-infected cells was used to identify it as the 6b protein. Further characterization revealed that it is a novel type of viral glycoprotein whose function is not clear. It is a soluble protein contained in microsomes; its slow export from the cell is caused by the presence of an endoplasmic reticulum (ER) retention signal at the C terminus. This amino acid sequence, KTEL, closely resembles the consensus KDEL signal of soluble resident ER proteins. A mutant 6b protein with the C-terminal sequence KTEV became resistant to digestion by endo-beta-N-acetylglucosaminidase H with a half-time that was reduced threefold. In contrast, a mutant with the sequence KDEL was completely retained in the ER. The FIPV 6b protein is the first example of a viral protein with a functional KDEL-like ER retention signal.