Mangiferin and Taurine Ameliorate MSRV Infection by Suppressing NF-κB Signaling

Natural product honokiol exhibits antiviral effects against Micropterus salmoides rhabdovirus (MSRV) both in vitro and in vivo

Micropterus salmoides rhabdovirus (MSRV) is a formidable pathogen, presenting a grave menace to juvenile largemouth bass. This viral infection frequently leads to epidemic outbreaks, resulting in substantial economic losses within the aquaculture industry. Unfortunately, at present, there are no commercially available vaccines or pharmaceutical treatments to combat this threat. In order to address the urgent need for therapeutic strategy to resist MSRV infection, the antiviral activity of natural product honokiol against MSRV was explored in this study. Firstly, cellular morphology was directly observed in an inverted microscope when treated with honokiol after MSRV infection. The results clarified that honokiol significantly lessened cytopathic effect (CPE) induced by MSRV and protected the integrity of GCO cells. Furthermore, the viral nucleic acid expression (G gene) was detected by reverse transcription real-time quantitative PCR (RT-qPCR) and the results indicated that honokiol significantly decreased the viral loads of MSRV in a concentration-dependent manner, and honokiol showed a high antiviral activity with IC50 of 2.92 μM. Besides, honokiol significantly decreased the viral titre and suppressed apoptosis caused by MSRV. Mechanistically, honokiol primarily inhibited the initial replication of MSRV and discharge of progeny virus to exert anti-MSRV activity. More importantly, in vivo experiments suggested that honokiol (40 mg/kg) expressed a fine antiviral activity against MSRV when administrated with intraperitoneal injection, which led to a notable 40% improvement in the survival rate among infected largemouth bass. In addition, it also resulted in significant reduction in the viral nucleic acid expression within liver, spleen and kidney at 2, 4 and 6 days following infection. What is more, 100 mg/kg honokiol with oral administration also showed certain antiviral efficacy in MSRV-infected largemouth bass via improving the survival rate by 10.0%, and decreasing significantly the viral nucleic acid expression in liver, spleen and kidney of largemouth bass on day 2. In summary, natural product honokiol is a good candidate to resist MSRV infection and has promising application prospects in aquaculture.

Exopolysaccharide secreted by Lactiplantibacillus plantarum Y12 showed inhibitory effect on the pathogenicity of Shigella flexneri in vitro and in vivo

Shigella flexneri is a prevalent foodborne and waterborne pathogen that threatens human health. Our previous research indicated that the Lactiplantibacillus plantarum Y12 exopolysaccharide (L-EPS) potentially inhibited the pathogenicity of S. flexneri. The in vitro results of this study demonstrated that L-EPS effectively mitigated the symptoms induced by S. flexneri in HT-29 cells, including inhibited gene expression levels of IL-1β, IL-6, IL-8, TNF-α, TLR 2/4, and NOD1/2; decreased apoptosis ratio; and alleviated damage degree of intestinal barrier function (Zona occludens 1, Occludin, and Claudin-1). The in vivo results demonstrated that S. flexneri treated with L-EPS elicited mild adverse physiological manifestations, an inflammatory response, and tissue damage. The infection of S. flexneri caused significant alterations in the abundance of phylum (Firmicutes, Bacteroidota, Actinobacteriota, and Proteobacteria), family (Lachnospiraceae, Muribaculaceae, Rikenellaceae, Prevotellaceaea, Ruminococcaceae, and Lactobaillaceae), and genus (Escherichia Shigella and Lachnospirillaceae NK4A136 group) within the cecal microbiota. These changes were accompanied by perturbations in taurine and hypotaurine metabolism, tricarboxylic acid (TCA) cycle activity, arginine biosynthesis, and histidine metabolic pathways. However, intervention with L-EPS attenuated the dysbiosis of cecal microbiota and metabolic disturbances. In summary, our research suggested a potential application of L-EPS as a functional food additive for mitigating S. flexneri infection.

Orange-spotted grouper IFNh response to NNV or MSRV and its potential antiviral activities

Type I interferon (IFN) plays a crucial role in the antiviral immune response. Nervous necrosis virus (NNV) and Micropterus salmoides rhabdovirus (MSRV) are the most important viruses in cultured larvae and juveniles, causing great economic losses to fish farming. To better understand the antiviral activities and immunoregulatory role of IFN from orange-spotted grouper (Epinephelus coioides), EcIFNh was cloned from NNV infected sample. EcIFNh has an open reading frame (ORF) of 552 bp and encodes a polypeptide of 183 amino acids. Phylogenetic tree analysis showed that EcIFNh was clustered into the IFNh branch. The tissue distribution analysis revealed that EcIFNh was highly expressed in the liver and brain of healthy orange-spotted grouper. The mRNA levels of EcIFNh were significantly upregulated after poly (I:C) stimulation and NNV or MSRV infection. Furthermore, the promoter of EcIFNh was characterized and significantly activated by EcMDA5, EcMAVS, EcSTING, EcIRF3, and EcIRF7 in the luciferase activity assays. We found that EcIFNh overexpression resisted the replication of NNV and MSRV, while EcIFNh silencing facilitated NNV replication in GB cells. In addition, EcIFNh recombinant protein (rEcIFNh) enhanced the immune response by inducing the expression of ISGs in vivo and in vitro, suggesting the potential application of rEcIFNh for anti-NNV and anti-MSRV. Taken together, our research may offer the foundation for virus-IFN system interaction in orange-spotted grouper.