Chikusetsusaponin IVa Protects against H9N2 Avian Influenza Virus Infection by Inhibiting Inflammation and TLR4/NF-κB Signaling Pathways in vitro and in vivo

Abstract

Background The prevalence of Hemagglutinin 9 Neuraminidase 2 (H9N2) avian influenza virus (AIV) in poultry in Asia has raised serious concerns about its zoonotic transmission and the potential for a pandemic, underscoring the need for effective therapeutics. Chikusetsusaponin IVa (CHS), a bioactive triterpenoid saponin from Radix saposhnikoviae, has exhibited anti-inflammatory activity in preclinical studies. We hypothesized that CHS could mitigate immunopathology during tumor necrosis factor (TNF)-infection by suppressing excessive inflammation. Objectives CHS is a natural saponin with anti-inflammatory activity. This research aimed to explore the in vitro and in vivo protective effects and mechanisms of CHS against H9N2 AIV infection. Materials and Methods We employed Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis and Gene Ontology (GO) analysis for the prediction of the underlying mechanisms, followed by a network analysis approach. In animal experiments, the toll-like receptor 4 (TLR4)/nuclear factor kappa B (NF-κB) signaling pathways and associated proteins were assessed using immunohistochemistry and western blot analysis. Results In A549 cells, CHS treatment reduced H9N2 AIV-induced apoptosis in a dose-dependent manner. CHS was found to have a suppressive effect on the mRNA expression of various inflammatory cytokines (including TNF-α, interleukin (IL)-6, IL-1β, and IL-8) as well as mediators such as inducible nitric oxide synthase (iNOS) and prostaglandin-endoperoxide synthase 2 (PTGS2). It can be seen that CHS does have anti-inflammatory effects. Bioinformatics analysis indicated that CHS might exhibit anti-inflammatory effects by modulating cytokine–cytokine receptor interaction and the NF-κB signaling pathways. Building upon this, it was found that CHS blocked the activation of TLR4 and NF-κB signaling pathways in A549 cells infected with H9N2 AIV. In vivo, CHS prolonged the survival time and increased the survival rate of H9N2 AIV-infected mice. CHS was found to have a protective effect on the lungs of infected mice, resulting in reduced damage and lower levels of viral load and inflammation. CHS inhibited the production of proinflammatory cytokines (IL-1β, TNF-α, IL-6, and IL-8) and inhibited the activation of TLR4 and NF-κB signaling pathways in the pulmonary tissues of mice that were infected. Conclusion CHS exerts protective effects against H9N2 AIV infection in vitro and in vivo. The anti-inflammatory mechanisms may involve the inhibition of cytokine production and the blockade of TLR4 and NF-κB signaling pathways.