ABSTRACT
Sikyungbanha-Tang (SKBHT) is a Chinese traditional medicine popularly prescribed to patients with respiratory inflammatory symptoms in Korea. Although the Korea Food and Drug Administration approved SKBHT as a therapeutics for relieving the symptoms, experimental evidence for SKBHT suppressing inflammation is scarce. Here, we presented evidence that SKBHT can suppress inflammation in an acute lung injury (ALI) mouse model and explored the possible underlying mechanisms of SKBHT's anti-inflammatory activity. Single intratracheal (i.t.) injection of SKBHT (1 mg/kg or 10 mg/kg body weight) into mouse lungs decreased prototypic features of lung inflammation found in ALI, such as a high level of proinflammatory cytokines, neutrophil infiltration, and the formation of hyaline membrane, which were induced by a single i.t. LPS (2 mg/kg body weight). When added to a murine macrophage RAW 264.7 cells, SKBHT activated an anti-inflammatory factor Nrf2, increasing the expression of genes regulated by Nrf2. SKBHT suppressed the ubiquitination of Nrf2, suggesting that SKBHT increases the level of and thus activates Nrf2 by blunting the ubiquitin-dependent degradation of Nrf2. SKBHT induced the expression of tumor necrosis factor α-induced protein 3 (TNFAIP3), an ubiquitin-modulating protein that suppresses various cellular signals to NF-κB. Concordantly, SKBHT suppressed NF-κB activity and the expression of inflammatory cytokine genes regulated by NF-κB. Given that Nrf2 and TNFAIP3 are involved in regulating inflammation, our results suggest that SKBHT suppresses inflammation in the lung, the effect of which is related to SKBHT activating Nrf2 and TNFAIP3.
ABSTRACT
BACKGROUND: Guettarda speciosa is mainly found in tropical areas in Asia. Although G. speciosa is traditionally used to treat some of the inflammatory disorders, the experimental evidence supporting the anti-inflammatory effect of G. speciosa is limited. Here, we sought to obtain evidence that G. speciosa has anti-inflammatory activity using an acute lung injury (ALI) mouse model and to explore possible underlying mechanisms for the activity. METHODS: The methanol extract of G. speciosa Linn. (MGS) was fingerprinted by HPLC. Cytotoxicity was determined by MTT and flow cytometer. As for an ALI mouse model, C57BL/6 mice received an intratracheal (i.t.) injection of lipopolysaccharide (LPS). The effects of MGS on lung inflammation in the ALI mice were assessed by differential cell counting and FACS of inflammatory cells and hematoxylin and eosin staining of lung tissue. Proteins were analyzed by immunoprecipitation and immunoblotting, and gene expression was by real-time qPCR. Neutrophil elastase activity was measured by ELISA. RESULTS: MGS did not cause metabolic disarray or produce reactive oxygen species that could induce cytotoxicity. Similar to ALI patients, C57BL/6 mice that received an i.t. LPS developed a high level of neutrophils, increased pro-inflammatory cytokines, and inflicted tissue damage in the lung, which was suppressed by i.t. MGS administered at 2 h after LPS. Mechanistically, MGS activated Nrf2, which was related to MGS interrupting the ubiquitin-dependent degradation of Nrf2. MGS suppressed the nuclear localization of NF-κB induced by LPS, suggesting the inhibition of NF-κB activity. Furthermore, MGS inhibited the enzymatic activity of neutrophil elastase. CONCLUSION: MGS could suppress lung inflammation in an ALI mouse model, the effect of which could be attributed to multiple mechanisms, including the activation of Nrf2 and the suppression of NF-κB and neutrophil elastase enzymatic activity by MGS.
