Objectives: Uncontrolled inflammation is an important factor in the occurrence and development of acute lung injury (ALI). Abnormal activation of NOD-like receptor thermal protein domain associated protein 3 (NLRP3) inflammasome and pyroptosis play a vital role in the pathogenesis of ALI. Palmatine (PAL), an isoquinoline alkaloid isolated from the traditional herb Fibraurea Recisa Pierre, was proved to show good anti-inflammatory properties. Herein, we investigated whether PAL could attenuate LPS induced ALI via inhibiting NLRP3 inflammasome activation and pyroptosis.

Methods: Phorbol myristate acetate (PMA)-induced THP-1 cells were first primed with LPS and then stimulated by PAL, followed by treatment with ATP. NLRP3 inflammasome was measured by enzyme-linked immunosorbent assay, quantitative reverse transcription polymerase chain reaction, western blotting, and immunofluorescence staining in vitro. In vivo, ALI was induced by intratracheal LPS-challenge combined with/without PAL treatment in C57BL/6 mice. Mice were intragastrically administered with PAL for 3 days. Lung tissue injury, inflammatory cell infiltration, bronchoalveolar lavage fluid (BALF) inflammatory factor secretion, lung wet/dry weight ratio (A/D), myeloperoxidase (MPO) activity, and NLRP3 inflammasome activation were assessed. Lung tissues were also subjected to perform transcriptomics and metabolomics sequencing, thereby further investigating the mechanism of PAL in ALI mice.

Results: PAL could significantly suppress NLRP3 inflammasome activation, IL-1β secretion and cell pyroptosis in THP-1 macrophages exposed to LPS. In the ALI mice model, RNA-sequencing identified NLRP3 and GSDMD were markedly upregulated after LPS exposure. PAL group showed significant differences in genes involved in the pathways of lymphocyte mediated immunity, immune response, canonical inflammasome complex and granzyme−mediated programmed cell death signaling pathway, which has been associated with cell pyroptosis. PAL could prominently improve the symptoms and pathological changes with reduced levels of TNF-α, IL-1β, IL-18 and IL-6 in BALF, and restrained NLRP3 inflammasome activation as well as pyroptosis. Additionally, the metabolic reprogramming of PAL on ALI mainly involved in β-Alanine metabolism, purine metabolism, sphingolipid metabolism, amino sugar and nucleotide sugar metabolism pathway.

Conclusions: PAL effectively inhibits NLRP3 inflammasome activation, reduces pro-inflammatory cytokine release, and suppresses pyroptosis, thereby ameliorates the progression of ALI. This study thereby established a solid foundation for further exploration into ALI therapy and the advancement and investigation of PAL.