Koumine ameliorates neuroinflammation by regulating microglia polarization via activation of Nrf2/HO-1 pathway

Background: Gelsemium elegans (Gardner & Chapm.) Benth (G. elegans) has been widely used as a traditional folk medicine in China and Southeast Asia. As the most abundant alkaloid in G. elegans, Koumine (KM) has been revealed the effect of inflammatory attenuation modulating by macrophage activation and polarization. Purpose: This study aimed to explore the effect of KM on modulation of microglia polarization that led to the suppression of neuroinflammation and further improved neurodegenerative behavior. Methods: Inflammatory mediators, microglia M1 and M2 phenotype markers and Nrf2/HO-1 pathway related protein were assessed in LPS-induced BV2 cells and LPS-treated mice by RT-PCR, immunohistochemistry, immunofluorescence and Western blotting. Moreover, the learning and memory abilities of mice were evaluated by Morris water maze test, and the neuronal damage was evaluated by the Nissl staining. Results: KM attenuated LPS-induced viability and morphological changes in BV2 microglial cells. Our findings showed that KM activated the Nrf2/HO-1 signaling pathway to promote phenotypic switch from M1 to M2 phenotypes. This switch suppresses the release of inflammatory mediators in LPS-induced BV2 cells. Meanwhile, KM attenuated neuroinflammation through modulating microglia polarization and subsequently reversed the behavioral alterations in LPS-induced mice model of neuroinflammation. Conclusions: KM may alleviate neuroinflammation by regulating microglia polarization with the involvement of Nrf2/HO-1 pathway, resulting of the neuroprotective effect.