Chikusetsusaponin IVa Targets Nrf2 to Inhibit H9N2 Avian Influenza Virus Infection

Background Chikusetsusaponin IVa (CHS) is a triterpenoid saponin that has been demonstrated to possess multiple properties. Objectives This study focused on inhibiting H9N2 avian influenza virus (AIV) by CHS and investigated the underlying mechanisms, specifically targeting the nuclear factor erythroid2-related factor 2 (Nrf2) signaling pathway. Materials and Methods The antiviral activity of CHS was evaluated by determining its half inhibitory concentration and therapeutic index (TI) in vitro . Markers of oxidative stress, encompassing superoxide dismutase, glutathione peroxidase, and malondialdehyde levels, were assessed. Analyses of pathways from the Kyoto Encyclopedia of Genes and Genomes and Gene Ontology were conducted to elucidate the underlying mechanisms, followed by network investigation and simulations of molecular docking. Moreover, the effects of CHS on Nrf2 and mitogen-activated protein kinase (MAPK) signaling pathways were assessed in human lung carcinoma A549 cells and a mouse model of H9N2 AIV infection. Results CHS showed inhibitory effects on H9N2 AIV in vitro , with TI values of 4.00 (co-treatment) and 6.29 (posttreatment). CHS reduced H9N2 AIV-induced oxidative stress and was predicted to target Nrf2, MAPK/phosphoinositide 3-kinase (PI3K)-protein kinase B (Akt) signaling pathways, and oxidation–reduction processes. Molecular docking analysis revealed a high affinity between CHS and Nrf2. In A549 cells, CHS enhanced Nrf2 activation, inhibited MAPK signaling, and reduced H9N2 AIV-induced oxidative stress. The therapeutic mechanism of CHS was found to be mediated by Nrf2. In a mouse model, CHS mitigated pulmonary impairment, improving the organism’s antioxidant activity. CHS also regulated the Nrf2 and MAPK signaling pathways in lung tissue. Conclusion CHS inhibits H9N2 AIV and alleviates virus-induced oxidative stress by targeting the Nrf2 signaling pathway. These observations lay the groundwork for devising prospective therapeutic interventions targeting H9N2 AIV infection.