All-Trans Retinoic Acid Attenuates Transmissible Gastroenteritis Virus-Induced Inflammation in IPEC-J2 Cells via Suppressing the RLRs/NF-κB Signaling Pathway

Transmissible gastroenteritis virus (TGEV) infection can cause transmissible gastroenteritis (TGE), especially in suckling piglets, resulting in a significant economic loss for the global pig industry. The pathogenesis of TGEV infection is closely related to intestinal inflammation. All-trans retinoic acid (ATRA) has anti-inflammatory activity and immunomodulatory properties, but it is unclear whether ATRA can attenuate the inflammatory response induced by TGEV. This study aimed to investigate the protective effect of ATRA on TGEV-induced inflammatory injury in intestinal porcine epithelial cells (IPEC-J2) and to explore the underlying molecular mechanism. The results showed that TGEV infection triggered inflammatory response and damaged epithelial barrier integrity in IPEC-J2 cells. However, ATRA attenuated TGEV-induced inflammatory response by inhibiting the release of pro-inflammatory cytokines, including IL-1β, IL-6, IL-8 and TNF-α. ATRA also significantly reversed the reduction of ZO-1 and Occludin protein levels induced by TGEV infection and maintained epithelial barrier integrity. Moreover, ATRA treatment significantly prevented the upregulation of IкBα and NF-κB p65 phosphorylation levels and the nuclear translocation of NF-кB p65 induced by TGEV. On the other hand, treatment of TGEV-infected IPEC-J2 cells with the NF-κB inhibitors (BAY11-7082) significantly decreased the levels of inflammatory cytokines. Furthermore, ATRA treatment significantly downregulated the mRNA abundance and protein levels of TLR3, TLR7, RIG-I and MDA5, and downregulated their downstream signaling molecules TRIF, TRAF6 and MAVS mRNA expressions in TGEV-infected IPEC-J2 cells. However, the knockdown of RIG-I and MDA5 but not TLR3 and TLR7 significantly reduced the NF-κB p65 phosphorylation level and inflammatory cytokines levels in TGEV-infected IPEC-J2 cells. Our results indicated that ATRA attenuated TGEV-induced IPEC-J2 cells damage via suppressing inflammatory response, the mechanism of which is associated with the inhibition of TGEV-mediated activation of the RLRs/NF-κB signaling pathway.

(+)-Catechin inhibition of transmissible gastroenteritis coronavirus in swine testicular cells is involved its antioxidation

Transmissible gastroenteritis virus (TGEV) causes transmissible gastroenteritis (TGE), especially in newborn piglets, which severely threatens the worldwide pig industry. In this study, (+)-catechin was evaluated for its antiviral effect against TGEV in vitro. Viability assays revealed that (+)-catechin treatment exerted a dose-dependent rescue effect in TGEV-infected ST cells, and this result was only obtained with the post-treatment application of (+)-catechin. The viral yields in (+)-catechin-treated cultures were reduced by almost three log₁₀ units. Quantitative real-time PCR analysis of the TGEV genome revealed that TGEV RNA replication was restricted after (+)-catechin treatment. Intracellular reactive oxygen species (ROS) detection showed that (+)-catechin alleviated ROS conditions induced by TGEV infection. Our results showed that (+)-catechin exerts an inhibitory effect on TGEV proliferation in vitro and is involved its antioxidation.

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(+)-Catechin has anti-TGEV effect.

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Anti-TGEV effect was working after TGEV infection.

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(+)-Catechin could relieve CPE caused by TGEV in ST cells.

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TGEV proliferation was decreased after (+)-catechin incubation.

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Antioxidation of (+)-catechin is related to its antiviral effect.

Transmissible gastroenteritis virus: identification of M protein-binding peptide ligands with antiviral and diagnostic potential

The membrane (M) protein is one of the major structural proteins of coronavirus particles. In this study, the M protein of transmissible gastroenteritis virus (TGEV) was used to biopan a 12-mer phage display random peptide library. Three phages expressing TGEV-M-binding peptides were identified and characterized in more depth. A phage-based immunosorbent assay (phage-ELISA) capable of differentiating TGEV from other coronaviruses was developed using one phage, phTGEV-M7, as antigen. When the phage-ELISA was compared to conventional antibody-based ELISA for detecting infections, phage-ELISA exhibited greater sensitivity. A chemically synthesized, TGEV-M7 peptide (pepTGEV-M7; HALTPIKYIPPG) was evaluated for antiviral activity. Plaque-reduction assays revealed that pepTGEV-M7 was able to prevent TGEV infection in vitro (p<0.01) following pretreatment of the virus with the peptide. Indirect immunofluorescence and real-time RT-PCR confirmed the inhibitory effects of the peptide. These results indicate that pepTGEV-M7 might be utilized for virus-specific diagnostics and treatment.

Putative probiotic Lactobacillus spp. from porcine gastrointestinal tract inhibit transmissible gastroenteritis coronavirus and enteric bacterial pathogens

A total of 310 bacterial strains isolated from the porcine gastrointestinal tract were tested for their activity against transmissible gastroenteritis (TGE) coronavirus and other enteric pathogens. Based on activity, the strains Probio-38 and Probio-37 were selected as potential probiotics and identified as Lactobacillus plantarum Probio-38 and Lactobacillus salivarius Probio-37 respectively by 16S rRNA gene sequencing. Supernatants of these strains inhibited TGE coronavirus in vitro in ST cells, without any cytopathic effect even after 72 h of incubation. Both the strains exhibited high survival in synthetic gastric juice. The strains were resistant to 5% porcine bile and exhibited antimicrobial activity against all the 13 enteric bacterial pathogens tested. These strains also exhibited resistance to most of the antibiotics analyzed. The inhibition of transmissible gastroenteritis coronavirus and enteric bacterial pathogens as well as the bile tolerance, high survival in gastric juice, and the antibiotic resistance indicate that the two isolated bacterial strains are ideal probiotic candidates for animal application after proper in vivo experiments.

Effect of chlorpromazine on experimental diarrhoea in just-weaned piglets

In just-weaned piglets (n = 30, 3-4 weeks) diarrhoea (100%) and vomiting (66%) were provoked by inoculation with transmissible gastroenteritis virus and enterotoxigenic E. coli strains (O149: K91: K88ac; LT, STa and STb enterotoxin positive). This combined infection resulted in a mortality of 71% within 7 days. During this period animals revealed a decrease in body weight, in arterial pressure, in leukocyte count, in plasma pH and in plasma lactic acid concentrations, and an increase in heart rate and in total plasma protein concentration. In shocked and expiring piglets an increase in haematocrit and a decrease in base excess and actual bicarbonate were observed. Chlorpromazine, administered intramuscularly on 3 successive days following the dual infection in 8 K88ac susceptible pigs, in a dosage of 2 and 1.5 mg/kg.24 h, somewhat retarded the appearance of severe diarrhoea and suppressed vomiting. These beneficial effects, however, did not result in an increased survival.

[Thymus-dependent nature of the antigens of enteropathogenic viruses]

The nature of antigens in enteropathogenic animal viruses--coronavirus--an agent of transmissive gastroenteritis of pigs (TGE) and pig enterovirus of serotype VI was studied. Basing on the results of the histomorphometric study of the white spleen pulp under the individual introduction of viruses and in combination with the lymphoid chalone it was established that the developing immune response has a thymus-dependent induction mechanism. The pharmacological stimulation of the T-system of animals suffering from virus gastroenteritis provides a positive therapeutic effect. The selective stimulation of the animal T-system may be considered as a promising trend in therapy of intestinal infections and as one of the possible ways to increase the immune response to the antigens of viral vaccines.

Effect of antisecretory drugs on experimentally induced weanling diarrhoea in piglets

In 45 newly-weaned 3 to 4-week-old piglets, diarrhoea was induced by a combined infection with transmissible gastroenteritis (TGE) virus and enterotoxigenic E. coli (ETEC) strains. In untreated control animals this dual inoculation resulted in profuse diarrhoea, vomiting, hypovolaemic shock and death of 77% of the animals within five days of TGE virus inoculation. Antisecretory drugs were administered intramuscularly for three consecutive days after experimental infection. The neurolepticum chlorpromazine, at 2 mg/kg/24 h, resulted in a significant inhibition of diarrhoea and vomiting, and in an increase in weight gain and survival. Sedation and hypothermia, however, were serious side-effects. The alpha 2 agonist clonidine, at 80 micrograms/kg/12 h, induced a significant antidiarrhoeal effect and a reduction in mortality. The drug, however, provoked decreased activity of alpha 2-adrenergic excitation and incoordination. The beta-adrenergic antagonist propranolol, at 0.33 mg/kg/8 h, and the calcium channel blocker verapamil, at 2 mg/kg/8 h, had no beneficial effect on the experimentally induced diarrhoea.

Pathophysiology of diarrhoea induced by a combined infection with transmissible gastroenteritis virus and enterotoxigenic Escherichia coli in newly-weaned piglets and the effect of flurbiprofen treatment

In newly-weaned 3-4 week old piglets (n = 29) diarrhoea (100%) and vomiting (65%) were induced by inoculation with transmissible gastroenteritis virus and enterotoxigenic E. coli strains (0(149):K91:K88ac; LT, STa and STb enterotoxin positive). This combined infection resulted in pronounced mortality within 7 days. During this period the piglets had decreases in body weight, arterial pressure and leucocyte count and increases in heart rate and in total plasma protein concentration. The plasma pH and lactic acid concentration decreased, whereas the values for pO2, pCO2 and frequency of respiration did not change significantly. No significant changes in the serum concentrations of potassium, chloride or calcium were observed, whereas sodium concentration revealed a transient increase. In shocked and dying piglets an increase in haematocrit was observed, whereas base excess and bicarbonate concentration decreased. Flurbiprofen, a potent non-steroidal anti-inflammatory drug, administered intramuscularly on 3 successive days following the combined infection at a dosage of 1 mg/kg/12 h was without beneficial effect on diarrhoea or mortality.

3-Substituted adenines. In vitro enzyme inhibition and antiviral activity

The direct alkylation of adenine at the 3 position has been extended to produce series of 3-alkyl-, 3-allyl-, and 3-(substituted benzyl)adenines. When these compounds were tested for enzyme inhibition and antiviral activity in vitro, 3-n-pentyladenine was found to be the most active compound in inhibiting the enzyme dopamine-beta-hydroxylase, and 3-(2-bromobenzyl)adenine showed the most striking inhibition of multiplication of Vaccinia virus and of Herpes simplex virus in tissue culture.

Evaluation of 6-azauridine and 5-iododeoxyuridine in the treatment of experimental viral infections

The potential antiviral activity of 6-azauridine and 5-iododeoxyuridine was evaluated in a coordinated study at five institutions. Experimental models in five species, the mouse, rabbit, swine, cat, and ferret, were established with use of 10 viruses: Herpesvirus hominis types 1 and 2, murine cytomegalovirus, vaccinia virus, Shope fibroma virus, transmissible gastroenteritis virus, swine influenza virus, feline viral rhinotracheitis virus, feline panleukopenia virus, and ferret distemper virus. Criteria for selection were: (1) representation from a number of major groups of viruses, (2) reproduction of natural routes of infection, and (3) simulation of potentially treatable viral infections of man. Antiviral activity was observed for 5-iododeoxyuridine in H. hominis infections in hairless mice and influenza in swine, and a slight degree of efficacy was noted in rabbits infected with Shope fibroma virus. Toxicity was also observed in most of the experimental models. There was a suggestion of antiviral activity with 6-azauridine in swine infected with transmissible gastroenteritis virus; however, enhancement of disease and some toxicity were seen in most of the other models. Efficacy of these two compounds was not well substantiated by these studies.

Isoprinosine: lack of antiviral activity in experimental model infections

This report is a condensation of data from a collaborative study proposed and sponsored by the Antiviral Substances Program of NIAID. The individual reports were prepared by the following persons: S. Baron and M. Worthington, NIAID, NIH; A. Friedman-Kien, New York University College of Medicine; J. C. Duenwald, Washington State University, L. A. Glasgow, M. Harmon, B. Janis, E. Kern, J. C. Overall, Jr., C. B. Smith, D. A. Stringfellow, and S. Westerberg, University of Utah College of Medicine; B. C. Easterday and E. H. Weinberg, University of Wisconsin.*

Recently there has been much interest in isoprinosine as a broad-spectrum antiviral compound. The activity of this substance was evaluated in a coordinated study at five institutions. Experimental models in five species of animals were established using 11 viruses. Criteria for selection were: (l) representation of most major groups of viruses, (2) reproduction of natural routes of infection, and (3) simulation of potentially treatable viral infections of man. No therapeutic effect could be demonstrated in infections with encephalomyocarditis virus, type 2 Herpesvirus hominis, influenza, and rabies viruses in mice; vaccinia virus in rabbits; rhinotracheitis and panleukopenia viruses in cats; distemper virus in ferrets; and influenza and transmissible gastroenteritis viruses in swine. The only antiviral activity observed in this extensive series of experiments was suppression of fibroma virus lesions in rabbits given 600 mg/ kg per day of isoprinosine. Although antiviral activity is not precluded in other viral infections in animals or in man, these results clearly fail to substantiate the potential of isoprinosine as a potent, broad-spectrum antiviral substance.