Piperlongumine mitigates LPS-induced inflammation and lung injury via targeting MD2/TLR4

Acute lung injury (ALI) is a fatal acute inflammatory illness with restricted therapeutic choices clinically. Piperlongumine (PL) is recognized as an alkaloid separated from Piper longum L, which was suggested to exhibit multiple pharmacological activities (e.g., anti-inflammatory activity). However, the effects of PL on LPS-triggered ALI and its anti-inflammatory target remain unclear. This paper intended to assess the roles of PL in LPS-triggered ALI, as well as its underlying mechanism and target. In vivo, ALI was induced by intratracheal injection of LPS to evaluate protective effects of PL and assessed by the changes of histopathological. In vitro, the anti-inflammatory activity and mechanism of PL were investigated by ELISA, RT-qPCR, transcription factor enrichment analysis, Western blotting and Immunofluorescence assay. The binding affinity of PL to MD2 was analyzed using computer docking, surface plasmon resonance, ELISA and immunoprecipitation assay. It was reported here that PL treatment alleviated LPS-induced pulmonary damage, inflammatory cells infiltration and inflammatory response in mice. In culture cells, PCR array showed that PL significantly inhibited LPS-induced inflammatory cytokines, chemokines, and type I IFNs genetic expression, along with the inhibition of TAK1 and TBK1 pathway. It is noteworthy that PL is capable of straightly binding to MD2 and inhibiting MD2/TLR4 complex formation and TLR4 dimerization. As revealed from this study, PL directly binding to MD2 to block cytokines expression by inhibiting the activation of TAK1 and TBK1 pathway, which then exerted its pulmonary protective activity. Accordingly, PL may act as an underlying candidate for treating LPS-triggered ALI.