Natural molecule Munronoid I attenuates LPS-induced acute lung injury by promoting the K48-linked ubiquitination and degradation of TAK1.

Acute lung injury (ALI) is a severe lung disease with limited therapeutic strategies. Munronoid I, a limonoid, which is extracted and purified from Munronia sinica, exhibits effective anti-neoplastic activities. In this study, we attempted to determine the anti-inflammatory effects of Munronoid I using both the lipopolysaccharide (LPS)-induced in vivo murine ALI models and in vitro assays. Our results demonstrated that Munronoid I treatment ameliorated LPS-induced ALI and inflammation in mice. Moreover, it also significantly inhibited LPS-induced pathological injuries, infiltration of inflammatory cells, and production of IL-1β and IL-6. Furthermore, the in vitro assay showed that Munronoid I could inhibit the LPS-induced expression of inflammatory mediators such as iNOS, COX2, and production of pro-inflammatory cytokines by suppressing the activation of NF-κB signaling pathway in mouse peritoneal macrophages. Munronoid I reduced the LPS-, tumor necrosis factor alpha (TNF-α)- or interleukin 1 beta (IL-1β)-induced transforming growth factor beta-activated kinase 1 (TAK1) phosphorylation and protein expression. Furthermore, the Munronoid I also promoted K48-linked ubiquitination and proteasomal degradation of TAK1. Taken together, these results demonstrated that Munronoid I exhibited anti-inflammatory activities both in vitro and in vivo, which might be a potential therapeutic candidate for the treatment of ALI and pulmonary inflammation.