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.