Dihydrotricetin from Euonymus hamiltonianus ameliorates neuroinflammation and exhibits neuroprotective effect in LPS-induced microglia

Microglia cells are the initial immune cells regulating neuroinflammation response. Under neuro-degenerative conditions, microglia exhibit as an over-activated phenotype, which generate large amounts of cytokines and inflammatory mediators. Euonymus hamiltonianus Wall. (E. hamiltonianus) showed an effect of enhanced memory and cognitive abilities in Alzheimer Disease (AD) model in our previous research. However, it is remained unknown about the anti-inflammation effect of E. hamiltonianus behind the neurodegenerative situation. The aims of the research are clarifying the possible therapeutic effects and its active compound of E. hamiltonianus on neuro-inflammation on the central nervous system. By the activity guided isolation, dihydrotricetin (compound 1) was identified as an active compound with BV-2 microglia and NMR Spectroscopy. In BV-2 LPS-induced microglial cells, compound 1 inhibited the pro-inflammatory factors, including Prostaglandin E2 (PGE2), interleukin (IL)-6, tumor necrosis factor (TNF)-α, and nitrite oxide (NO) production. This suppressed the activation of microglia in LPS-injected mouse cortex. Besides, the research indicated that compound 1 inhibited PI3K/AKT/IκB/NF-κB and MAPK pathways, and further promoted the inhibition of NLRP3 signaling activation. This research determined that compound 1 is involved in the NRF2/HO-1 signaling and anti-oxidative activity. These data suggest that compound 1 can be a key regulator of microglial activation in LPS-induced neuro-inflammation in vivo and in vitro.