Time-dependent changes in NLRP3 and Nrf2 levels in lipopolysaccharide-induced acute lung injury

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are severe clinical conditions with a high mortality rate. Nucleotide-binding oligomerization domain (NOD)-like receptor containing pyrin domain 3 (NLRP3) and nuclear factor E2-related factor 2 (Nrf2) have been reported to be associated with ALI. However, the dynamic changes in the levels of these factors in lipopolysaccharide (LPS)-induced lung injury remain unclear. Thus, the present study aimed to determine the LPS-induced activation of immunological cascades, as well as the NLRP3/Nrf2 signaling pathway at different stages of lung injury. For this purpose, mice were divided into six groups as follows: The control, LPS-4 h, LPS-24 h, LPS-48 h, LPS-96 h and LPS-144 h groups. LPS (4 mg/kg) was administered intratracheally to induce lung injury. Flow cytometry was used to determine the changes in macrophages, neutrophils and T-cell subsets in lung tissue, hematoxylin and eosin staining were used to measure the histopathological changes in lung tissues, ELISA was performed to evaluate the levels of cytokines, western blot analysis was used to measure the levels of inflammatory proteins, and reverse transcription-quantitative PCR used to determine the mRNA level of a target gene. Following LPS administration, evident histopathological damage with neutrophil infiltration was observed which peaked at 48 h. The levels of interleukin-1β, keratinocyte-derived chemokine, macrophage inflammatory protein 2 and tumor necrosis factor a were markedly increased in bronchoalveolar lavage fluid and serum from the mice, and these levels peaked at 4 h. Moreover, LPS promoted Toll like receptor-4 expression and reactive oxygen species production, thus activating NLRP3/Nrf2 signaling and pyroptosis. Collectively, the present study demonstrates that LPS triggers multiple inflammatory molecules and immune cells during ALI, which may be closely involved in the irregular redox status, NLRP3/Nrf2 pathway and pyroptosis.