Suppression of lung inflammation by the methanol extract of Spilanthes acmella Murray is related to differential regulation of NF-κB and Nrf2.

ETHNOPHARMACOLOGICAL RELEVANCE

Although Spilanthes acmella has been used to relieve inflammation, fever, pain, or infection in traditional Asian medicine, experimental evidence supporting these functions is scarce. Here, we examined an anti-inflammatory function and a possible underlying mechanism of S. acmella Murray (SAM).

MATERIALS AND METHOD

The methanol extract of SAM was fingerprinted by HPLC. C57BL/6 mice were administered with a single intratracheal (i.t.) LPS and 2 h later with a single i.t. SAM. The effect of SAM on lung inflammation was assessed by histology, semi-quantitative RT-PCR, and MPO assay of lung tissue. The effects of SAM on a pro-inflammatory factor NF-κB and an anti-inflammatory factor Nrf2 were analyzed by immunoblotting of nuclear proteins and by semi-quantitative RT-PCR analysis of mRNA of the genes governed by these transcription factors. V5-Nrf2 was precipitated by an anti-V5 antibody and the ubiquitinated V5-Nrf2 was revealed by immunoblotting of HA-tagged ubiquitin.

RESULTS

The i.t. SAM robustly diminished a neutrophilic lung inflammation induced by i.t. LPS treatment of mice. In RAW 264.7 cells, SAM suppressed the nuclear localization of NF-κB and the expression of NF-κB-dependent cytokine genes. SAM increased the level of Nrf2 in the nucleus and the expression of Nrf2-dependent genes while suppressing ubiquitination of Nrf2.

CONCLUSION

Our results suggest that SAM can suppress a neutrophilic inflammation in mouse lungs, which is associated with suppressed NF-κB and activated Nrf2. Our results provide experimental evidence supporting the anti-inflammatory function of S. acmella.