Natural bear bile powder suppresses neuroinflammation in lipopolysaccharide-treated mice via regulating TGR5/AKT/NF-κB signaling pathway

According to the Tang Dynasty classics Dietetic Material Medica and the Ming Dynasty classics Compendium of Materia Medica records, bear bile powder (BBP) has been used to treat a variety of diseases, such as febrile seizures, the pathogenesis of which is associated to neuroinflammation. However, the mechanism of BBP on alleviating neuroinflammation remains unclear.Microglia can be activated by peripheral lipopolysaccharide (LPS) and play an important role in the pathogenesis of neuroinflammation. The purpose of this study is to investigate the effects and mechanism of BBP in inhibiting LPS-induced microglia inflammation in vitro and in vivo.The anti-microglia inflammatory effects and mechanism of BBP were assessed in LPS-treated BV2 microglial cells and in LPS-treated mice. The mRNA expression levels of the inflammatory factor and the protein expressions of cyclooxygenase-2 (COX2), inducible nitric oxide synthase (iNOS), takeda G-protein coupled receptor 5 (TGR5), nuclear factor-κB (NF-κB), inhibitor of NF-κB (IκBɑ), protein kinase B (AKT) in BV2 cells, mouse hippocampus and cortex were detected. The NF-κB transcription activity and NF-κB nuclear translocation were observed.Our findings showed that BBP reduces branched process retraction and NO in LPS-treated BV2 cells, inhibits the protein expression of ionized calcium binding adaptor molecule 1 in the hippocampus of LPS-treated mice. Moreover, we observed that BBP decreases tumor necrosis factor α, interleukin (IL)-6 and IL-1β mRNA levels, deceases iNOS and COX-2 protein levels, increases TGR5 protein levels, suppresses the phosphorylation of AKT, NF-κB and IκBɑ protein in microglia both in vitro and in vivo. Further, we found that triamterene, the inhibitor of TGR5, abolishes the effects of BBP in LPS- treated BV2 cells.BBP inhibits LPS-induced microglia activation, and the mechanism of its action is partly through TGR5/AKT/NF-κB signaling pathway.