<i>Viola tianshanica</i> Maxim Extract Ameliorates Lipopolysaccharide Induced Acute Lung Injury by Regulating NLRP3 Inflammasome and Nrf2 Signaling Pathway

Acute lung injury (ALI) is a prevalent critical respiratory disease associated with high morbidity and mortality rates. <i>Viola tianshanica</i> Maxim has been traditionally employed in Uygur medicine for treatment of various respiratory diseases. <i>Viola tianshanica</i> Maxim extract (VTM) has strong anti-inflammatory and anti-oxidant properties, and its potential protective mechanism against ALI is worthy of further study. In this study, we investigated the protective effect of VTM on lipopolysaccharide (LPS)-induced ALI in mice and explored its underlying mechanisms involving NOD-like receptor protein 3 (NLRP3) inflammasome and Nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathways. VTM was extracted from <i>Viola tianshanica</i> Maxim. Chemical compositions of VTM were identified by HPLC-HRMS/MS. The protective effect and molecular mechanisms of VTM on alleviating ALI were verified by hematoxylin-eosin (H&E) staining, enzyme-linked immunosorbent assay (ELISA), quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot. A total of 13 chemical compositions were analyzed and identified from VTM, including esculetin, isoschaftoside, kaempferol-7-O-β-D-glucopyranoside, among others. VTM effectively alleviated ALI by reducing of the wet-to-dry weight (W/D) ratio, serum inflammatory cytokines PGE2 and LTB4 levels, and lung tissues IL-1β, IFN-γ, TNF-α and MCP-1 levels. VTM significantly decreased mRNA expressions of IL-6, TNF-α and MCP-1, inhibited MDA and MPO formation, and reversed SOD and GSH depletion. Meanwhile, VTM markedly improved histopathological changes, inhibited NLRP3 inflammasome activation by reducing the protein and mRNA expression levels of NLRP3, Caspase 1, GSDMD and IL-1β in lung tissues. Additionally, VTM mitigated oxidative stress in ALI by upregulating the protein and mRNA expression levels of Keap1, Nrf2 and HO-1 in lung tissues. Our findings indicated that pretreatment with VTM prevented LPS-induced ALI by regulating NLRP3 inflammasome and Nrf2 signaling pathway.