ABSTRACT
BACKGROUND: Butyrate acts as a regulator in multiple inflammatory organ injuries. However, the role of butyrate in acute liver injury has not yet been fully explored. In the present study, we aimed to investigate the association between butyrate and lipopolysaccharide (LPS)-induced acute liver injury and the signaling pathways involved. METHODS: LPS-induced acute liver injury was induced by intraperitoneal injection of LPS (5 mg/kg) in G-protein-coupled receptor 43 (GPR43)-knockout (KO) and wild-type female C57BL/6 mice. Sodium butyrate (500mg/kg) was administered intraperitoneally 30â¯min prior to LPS exposure. Liver injury was detected by serum markers, tissue morphology, and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL). Pro-inflammatory-factor levels were detected by enzyme-linked immunosorbent assay and real-time polymerase chain reaction (RT-PCR). Cell models were first treated with sodium butyrate (4 µmol/mL), followed by LPS (1 µg/mL) half an hour later in GPR43 small interfering RNA (siRNA)-transfected or control RAW264.7 cells. Cell-inflammation status was evaluated through detecting pro-inflammatory-factor expression by RT-PCR and also through checking toll-like receptor 4/nuclear factor-κB (TLR4/NF-κB)-element levels including TLR4, TRAF6, IKKß, IкBα, phospho-IкBα, p65, and phospho-p65 by Western blot. The interaction between GPR43 and ß-arrestin-2 was tested by co-immunoprecipitation. RESULTS: Sodium butyrate reversed the LPS-induced tissue-morphology changes and high levels of serum alanine aminotransferase, aspartate transaminase, myeloperoxidase, TUNEL, and pro-inflammatory cytokines such as tumor necrosis factor-α and interleukin-6. The ameliorating effect of sodium butyrate was weakened in GPR43-KO mice and GPR43 siRNA RAW264.7 cells, compared with those of GPR43-positive controls. Sodium butyrate downregulated some elements of the TLR4/NF-κB pathway, including phospho-IκBα and phospho-p65, in RAW264.7 cells. Increased interactions between GPR43 and ß-arrestin-2, and between ß-arrestin-2 and IкBα were observed. CONCLUSION: Sodium butyrate significantly attenuated LPS-induced liver injury by reducing the inflammatory response partially via the GPR43/ß-arrestin-2/NF-κB signaling pathway.
ABSTRACT
AIM: To study the role and the possible mechanism of ß-arrestin 2 in lipopolysaccharide (LPS)-induced liver injury in vivo and in vitro. METHODS: Male ß-arrestin 2+/+ and ß-arrestin 2-/- C57BL/6J mice were used for in vivo experiments, and the mouse macrophage cell line RAW264.7 was used for in vitro experiments. The animal model was established via intraperitoneal injection of LPS or physiological sodium chloride solution. Blood samples and liver tissues were collected to analyze liver injury and levels of pro-inflammatory cytokines. Cultured cell extracts were collected to analyze the production of pro-inflammatory cytokines and expression of key molecules involved in the TLR4/NF-κB signaling pathway. RESULTS: Compared with wild-type mice, the ß-arrestin 2 knockout mice displayed more severe LPS-induced liver injury and significantly higher levels of pro-inflammatory cytokines, including interleukin (IL)-1ß, IL-6, tumor necrosis factor (TNF)-α, and IL-10. Compared with the control group, pro-inflammatory cytokines (including IL-1ß, IL-6, TNF-α, and IL-10) produced by RAW264.7 cells in the ß-arrestin 2 siRNA group were significantly increased at 6 h after treatment with LPS. Further, key molecules involved in the TLR4/NF-κB signaling pathway, including phospho-IκBα and phosho-p65, were upregulated. CONCLUSION: ß-arrestin 2 can protect liver tissue from LPS-induced injury via inhibition of TLR4/NF-κB signaling pathway-mediated inflammation.
