Icariin and icaritin ameliorated hippocampus neuroinflammation via inhibiting HMGB1-related pro-inflammatory signals in lipopolysaccharide-induced inflammation model in C57BL/6 J mice

Inflammation is a defensive response of the body and is at the center of many diseases' process like depression. High mobility group protein box 1 (HMGB1), has been proved to function as a pro-inflammatory cytokine. We aim to explore the role of HMGB1 played in the neuroinflammation here. In this study, we used LPS to induce an acute inflammatory response, and to measure the anti-neuroinflammation effect of icariin (ICA) and icaritin (ICT). We found that LPS could increase the expression of HMGB1 in serum and hippocampus, along with a high expression of HMGB1 in the cytoplasm and a high expression of RAGE, which could be rescued by ICA and ICT, and ethyl pyruvate (EP) pretreatment showed similar effects here. We speculated that the translocation of HMGB1 from the nucleus to the cytoplasm played an important role in neuroinflammatory process, and HMGB1-RAGE signal was involved in this process. Furthermore, we found that ICA and ICT treatment activated TLR4-XBP1s related NF-kappa B signal, which we thought was relevant with the neuroprotective effect of ICA and ICT. However, EP pretreatment suppressed TLR4-XBP1s-endoplasmic reticulum stress related NF-kappa B signal to anti-inflammatory response, which was almost absolutely opposite with ICA and ICT treatment. We speculated that it might be caused by the duration of inflammation. We supposed that ICA and ICT could ameliorate neuroinflammation in hippocampus via suppressing HMGB1-RAGE signaling and might show a neuroprotective effect via activating TLR4-XBP1s related NF-kappa B signal at the same time, making it possible to act as an anti-neuroinflammatory drugs.