Sodium houttuyfonate induces bacterial lipopolysaccharide shedding to promote macrophage M1 polarization against acute bacterial lung infection.

Sodium houttuyfonate (SH), derived from the widely utilized natural herb Houttuynia cordata, exhibits an effective therapeutic effect on various diseases, including bacterial and fungal infections, especially the respiratory tract infection. Therefore, the anti-microbial mechanisms of SH may be different from the single-target action mechanism of conventional antibiotics, and further research is needed to clarify this. Firstly, we discovered that SH can effectively intervene in mouse lung infections by reducing bacterial load and acute inflammation response related to pneumonia caused by Pseudomonas aeruginosa. Interestingly, our results confirmed that SH has surface activity and can directly induce changes in the cell wall the shedding of surface lipopolysaccharide (LPS). Additionally, we found that SH-induced shedding of LPS can induce M1 polarization of macrophages in the early stage, leading to the production of corresponding polarization effector molecules. Subsequently, we discovered that SH-induced M1 polarization cells can effectively phagocytose and kill bacterial cells. The protein expression results indicated that SH can enhance the expression of M1 polarization pathway of TLR4/MyD88/NF-κB during the initial phase of macrophage and pathogen interaction. In summary, our results imply that SH could directly induce the shedding of P. aeruginosa LPS in a surfactant-like manner. Afterwards, the SH induced abscisic LPS can initiate the TLR4/MyD88/NF-κB immune pathway to trigger the M1 polarization of macrophages, which might intervene the P. aeruginosa-caused acute lung infection at early stage. Based on these findings, we attempted to coin the term "immune feedback eradication mechanism against pathogen of natural product" to describe this potent antimicrobial mechanism of SH.